f77 - f77 is a superset of FORTRAN 77. Very Good Standard compiler.
Type man f77 for more details.
f90 - Fortran 90 compiler. Fortran 90 has good features of
C and Fortran 77.
Type man f90 for more details.
Simple Instructions
Suppose your Fortran file is called prog.f then
f77 prog.f
will produce an executable (assuming you have made no errors) called a.out which you can run simply by typing a.out.
*** Use g77 in place of f77 if you do not have f77! ***
Check LS Fortran