To access the project area in RTC you should have received a welcome email with the necessary link to connect to the project area in a web browser. Also this email should contain a team invitation section that has all the settings that you can copy in the Eclipse client of RTC. It should look like this:
teamRepository=https://jazz.net/sandbox01-ccm
userId=yourid
userName=Your Name
projectAreaName=Your Project (Change and Configuration Management)

in the Eclipse Client of RTC you can just use the "accept team invitation link" on the welcome page and copy and paste the settings from your email. After that you should have connection with your repository and your project area.

The sandbox environment has everything defined for you in regards of process template, work item types etc. you do not have to care for that at the moment. But there is no content, that means you should first define some work items, some plans and maybe some source code.
If you look for guidance on how to do that, have a look in the tutorials section of the documentation under this link:
http://pic.dhe.ibm.com/infocenter/clmhelp/v4r0/index.jsp?topic=%2Fcom.ibm.help.common.nav.doc%2Ftopics%2Ftutorials.html

There are several sections with many lessons to start with. But be careful: There is now order in the Tutorials. The different chapters are organized by theme. You should first look for "Planning projects" and "Defining work items" or "Change Management". Select the tutorials that look interesting to you and start.

Hope that helps.