Web pages available on the net are the SRC M3 home page and another good page in Europe I can't find right now.
The man pages just point to the SRC implementation pages but nevertheless are in /usr/contrib/man (add that to your MANPATH).
In the current release, m3 is only intended to be run by m3build. m3build lives is in /afs/cs/project/spin/bin. m3 and the installed packages/libraries are in /afs/cs/project/spin/lib/m3. When you do a complete system build, you get your own.
NOTE: The compile in /afs/cs/project/spin/bin is a pristine DEC SRC Modula-3 compiler. It does not contain the local changes that we have made to support SPIN. The local spin compiler can be found in /afs/cs/project/spin/build/latest/export/bin/. It's probably quite a task to just use this compiler all by itself unless you have a whole SPIN tree checked out.
The right thing to is add /afs/cs/project/spin/bin to your path and start by making a new program and then compiling it. The pages at SRC explain how to do this.
For instructions on how to write Modula-3 programs, see here