Step One: Construct the Platform
We use the word platform to indicate all of the dependencies of the project, gathered together and unzipped into the same directory. This is really just an Eclipse installation, just like the one that you will most likely have on your local disk. So, there's a good chance that the Eclipse installation you already have will do the trick, but if you want to use the exact versions that STP builds against, here are the details.
Download all of the required pieces of the platform and expand them onto your disk. The location will be your platform directory. The platform bills of materials above should give you everything you need to build any of the STP sub-projects and components. You can get away with less if you only want to build one of the STP sub-projects.