how i can save and run FORTRAN program in dos?

Answer 1

You write your fortran programs using a text editor and then save them on your computer, probably as a text file.
You now need a compiler to compile your fortran program.
Once compiled it will create an executable module or .exe file that you can run from a command window.

All you have to do is purchase a fortran compiler and follow the instructions on how to use it.