You should at this point have a working Sakai installation. Now it's time to get started with adding users, creating work sites, and otherwise playing around with the tools. We won't try to present a full user's guide here, but we can offer some pointers to get you oriented and on your way, and link you to more exhaustive sources of information elsewhere.
When Tomcat has come up successfully, you should be able to direct your browser to its gateway page at http://localhost:8080/portal (or replace 'localhost' with the name of the server where it's installed). From the gateway page you can create new accounts or browse for public site content. You could start by creating a new account, but that can also be done as an admin, and since the admin functions are needed to allow this account the right permissions, it's just as well to start by logging in as the admin user. Sakai's out-of-the-box admin account is simply named 'admin' (with password also 'admin'), so use those credentials to log in.
Every user on the system - including the admin - has a private site called My Workspace. It's the landing point upon logging in, and it's the first site tab visible at the upper left. Running vertically along the left-hand side of the screen are links to the various different tool pages within a given site, and the admin's My Workspace has a different set of such options here than most (each different type of account can be configured to have a different set of tools in its My Workspace by altering a template - see below).
Each new (accessible) site becomes visible as a tab along the top, to the right of My Workspace. For most users, they initially only have access to one site - their My Workspace. The admin user is a little different, in that it has access to two.
The second admin site (which you can enter by clicking on its tab) is entitled Administration Workspace which, strangely enough, looks exactly the same as the admin My Workspace. It is.
Why the redundancy? Because you'll likely want to make these admin tools available to a particular user who doesn't have access to the admin's My Workspace (no one has access to other people's My Workspace on the system). To allow anyone access to the admin tools, you need only add them to the list of users of the Administration Workspace, and then promote them in the site to the "admin" role.
The first thing you may want to do is to change the admin password to something secure, and to start creating a few sample users on your system. You can do both of those tasks through the Users tool on the left. To change the admin user's password, simply click on the 'admin' username in the list of users, and edit the fields on the subsequent page. To create users, click on the New User action link at the top of the tool page.
If you're itching to create your first worksite, you may be tempted to dive directly into the Sites tool. That would probably be a mistake. The Sites tool is a powerful way to construct an entire site from the ground up, with fine-grained control over its every page, tool, and configuration detail. But this flexible power comes with a price, making for an intimidating interface and epic-scale workflow. The Sites tool is therefore best used as a way to tweak an existing site after the fact, once the standard pieces have been more expediently assembled.
The best way to start creating sites, therefore, is to use the Worksite Setup tool. Click on the New link at the top of the tool page, and then, for simplicity's sake, choose the Project site type, which will allow you to avoid issues of academic term, etc., that are provoked by a "course" site - issues which are probably unnecessary if you just want to start playing with the tools. Either type of site will serve, however: both types of sites have all the tools available to them.
Step through the remaining site creation pages, making your preferred selections. Be sure to click the Create Site button at the end of the process. After doing so, you should see the site title visible as a new tab along the top of the screen.
Since you set this site up as an admin, the admin is technically the owner of this site, and its only member at first. If you want to add other sample users to this site in different roles, you can do so through the Site Info tool of the site itself.
Click on the tab of your new site (which should now be visible) to enter it, and then click on the Site Info link along the lefthand side. Site Info has a number of site maintainer functions available as action links across the top, and Add Participants is the one that will allow you to connect other users to the site. These users will of course need to have been previously created.
As long as we're here in Site Info, it's worth pointing out that the Edit Tools link at the top will allow you to remove and add tools from the site.
You may have noticed an extra tool appear in your site - one which you didn't explicitly choose - labeled Help. This tool provides online documentation of the various bundle tools, and other facets of the system. This should be your companion as you learn more about the software's functionality.
This Help tool is also reached in a context-sensitive way by clicking on the question mark icons at the upper right of any particular tool frame. Clicking on those question marks will open up the precise content of the tool you happen to be in at the time.
At some later point, when you become comfortable with the standard tools, you may wish to see other, more experimental tools that are available for Sakai. The Sakai distribution includes provisional tools that are still maturing, but can already serve needs in innovative ways that the standard ones do not. These extra tools require additional steps to enable, so that system users will not stumble across them inadvertently if that's not desired, but you are encouraged to evaluate them for your own deployment. See http://bugs.sakaiproject.org/confluence/display/DOC/2.3+Sakai+Tools for more details.
Sakai information has been unfortunately a little fragmented to date. Attempts are underway to consolidate and present this information in a more uniform way, but in the interim a tourist's guide of the landmarks may be in order.
The sakaiproject.org site offers the best background and orientation to the project and its goals, but chances are you've already seen it. For more particular information on the progress and roadmaps of certain tools or other initiatives, see the Confluence space named Management/Project Coordination. That coordinating page will also link you out to Confluence spaces for particular tools, and documentation about them.
The Sakai community hosts its own Sakai installation to serve up collaboration sites for its various sub-groups, and for direct interaction with community members you should join sites there that may be of interest. You can create an account there by visiting http://collab.sakaiproject.org and clicking on the New Account button. Once your account is created you can log in, and with the Membership tool you may join any worksites that may seem appropriate. Joining a site automatically adds you to its email list, and unjoining a worksite similarly removes you (while, it should be noted, sending an "unsubscribe" email will not).
Reference materials for various technical issues are best found in Sakai's
subversion repository (where these installation documents are also stored) or in
the project's Confluence wiki. The docs in subversion can be found in the reference
module, e.g. https://source.sakaiproject.org/svn/reference. See in particular the
docs/architecture folder contained there, which
contains a wide-ranging collection of technical white papers.
The Confluence wiki is a more informal source of information, but also valuable and broader in scope. New developers in particular should visit the Programmer's Cafe, while the Sakaipedia provides nuggets of insight on a wide array of issues. You're encouraged to create an account there and participate.
But often the most incisive information comes from direct interaction with your peers. As mentioned above, the Collab Server is the place to go for this. For technical questions the best (and most active) such group is DG: Development, also commonly referred to by its alias, "sakai-dev."