The first step is to look over config.h.in and make sure that the few manual configuration options are correct for your system. These are listed at the top of the file.
The second step is to run
configure
It has a few options worth noting:
--prefix=<install path prefix>
--with-cursesinclude=<path to curses.h dir>
Things to watch for: While configure is running, you should make sure that it finds your mail spool correctly, and also that it finds your correct domain name. If it does not, you should make sure to edit config.h to correct the errors before you continue.
Now you are ready to starting compiling. Type:
make
Mutt should compile cleanly (without errors) and you should end up with a binary called mutt.
To actually install it (not required except if your spool directory is SETGID), type:
make install
.