Okay, here's a simple overview.
Basically, the equipment you need depends on the kind of tape, since there are a number of different formats and you'll obviously need something that can play it back correctly. If it's just a cassette, all you really need is a decent deck.
If it's open reel, things get a bit more complicated - we'd really need more information about them to make a more sensible suggestion. There is also the fact that the tapes may have deteriorated, which requires some preparation before playing them.
Either way, once you have a machine capable of playing the tapes back correctly, it's just a matter of digitizing them with something like Goldwave or whatever and a decent soundcard. It's best practice to record and store them as .WAV files, since MP3 compresses audio by losing information. You can convert the .WAVs to .MP3 format as needed, but you can't properly go back from MP3 to WAV if you need to do so later.