Do you have a manual to the 4-track? If so, then the manual will explain everything you need to know to get started.
Typically you would put a microphone in one of the 4-track's main inputs, select which of the four tracks to which you want to record, plug your headphones into the headphone jack and start playing. Then you can rewind the tape, switch to another track to record and hit record. You will hear your previous recording while you can record on the second track.
To hear it on stereo speakers, you would plug the main outputs (usually RCA, or stereophone sized) into the line inputs of your stereo (cd, vcr, tape, etc. but NOT phono).
You will need a microphone to record acoustic guitar, but you can record electric guitar directly into the 4-track. It won't sound too good if you just plug the guitar in. If you want to use an amp, you would run a cable from the line out of your amp to your four-track (do NOT use the speaker out on the amp. It will fry your 4-track).
Hope this helps,
Cy