hallo,
just as with any (or most) of the other plugins: Exit eclipse, then just unpack ist to the appropriate directory, this is your eclipse directory. Some of the files the will in the plugins directory and some in the features dir.
Start eclipse and anything should be working. You then have to associate your projet with clearcase (right mouse click on the project, ->team->) – you must have created the clearcase project with the actual clearcase tool.
regards. Jürgen