For more details, there's also the manual entry for gsi.
BTW: I don't know about the Fedora RPM, but I found that the Ubuntu repository's Gambit-C was quite outdated (4.0-ish), with missing features like simple compilation of stand-alone executables. The most recent version is 4.6. If your RPM's version is a few decimal places behind, I'd suggest just installing from source; it's a pretty standard configure -> make -> make install sequence. Just remember the following option when running configure:
./configure --enable-single-host
This speeds things up quite a bit.