That's not so simple. ST and MSA are disk image files, which may contain multiple files, directories. But may be that there are no files at all.
What you can do with image files is to extract files, compete directories from them.
Here is SW what can do it:
http://atari.8bitchip.info/floimgd.phpIf you don't have floppy drive in PC, you don't need to install fdrawcmd driver. Will get error message at start about missing driver, but you can work with image files. Open Another Image File selects ST or MSA file, and then you can go in File transfer to see files, and extract them.
Work with MSA files may be little simpler - in case of ST files may need to set self disk geometry, what requires some practice.
Conversion to executables is not possible with some SW, that's complicated process.