If you've got multiple C compilers installed, you'll have your choice of which one to use. Various older versions of Dec C had some gotchas, so if you're using a version older than 5.2, check the Dec C Issues section. Once you issue your MMS command, sit back and wait. Perl should build and link without a problem. If it doesn't, check the Gotchas to watch out for section.
Instructions are in the Mailing Lists section.
Once Perl has built cleanly, you need to test it to make sure things work. Testing is very easy, though, as there's a full test suite in the perl distribution. This may take some time, as there are a lot of tests. If any tests fail, there will be a note made on-screen. At the end of all the tests, a summary of the tests, the number passed and failed, and the time taken will be displayed.