Since you said that you "downloaded the Tomcat plugin", I figure that you did one of two things:
1. Downloaded Tomcat and placed it in the Eclipse plugin folder. Tomcat isn't the tomcat plugin, so you shouldn't do that. Tomcat should be installed in a directory that's completely external to Eclipse.
2. Downloaded a third-party Tomcat manager such as the sysdeo plugin. I know sysdeo pretty well, but it's not the only Tomcat plugin available, and they will differ on how you configure them.
The WTP plugin comes already installed when you download and install the
J2EE spin of Eclipse Indigo. But personally, I hate it, so I install sysdeo and ignore WTP.
In the particular case of the sysdeo plugin, it will add icons to your toolbar like you described, as well as equivalent menu controls. To actually use it, you must employ the Window/Preferences menu and select the Tomcat options. You'll have to tell the plugin where your Tomcat home directory is, which version of Tomcat it is, and various other minor details. If you have existing Eclipse web projects that you want to be able to debug in tomcat, select them in the Tomcat/source path preferences topic.
