To convert a basic program to a compiled executable you'd need a copy of the basic compiler program.
It shouldn't matter what filename you give when saving your basic program to file. To run a basic program from the dos prompt, type the basic program command, space, the name of your basic program file, enter. Here's documentation on using microsoft basic. Gw-basic is the non ibm version of ibm basic, otherwise the same thing.
http://www.antonis.de/qbebooks/gwbasman/