The first sensible thing to do is to download it. Once you have your MockMakerEclipsePlugin.zip, just unpack it to the eclipse/plugin folder
Then exit and relaunch eclipse.
Open the java browsing perspective, right click on an interface or a class and you will see a mockmaker menu in the pulldown, as shown here:
Once there, choose the package you want the mockobject to be created in
Press ok and the MockObject will be generated...