Best adivce I can think of is
1. Do some reading on the topics
2. Do some testing (read: playing around) with the tools you have, one at a time to get a good feel for how they work and what they do.
You want to make sure you know what each tool is for before you get too crazy playing around though (I've lost many an hour this way)
I'm not familiar with goldwave, but the terms are pretty-much interchangeable.
Basically...
Compressors bring up the volume on soft parts and leave the louder parts alone. There are entire books written on compression - there's a lot, lot more to it than that, but that's the genderal idea. It's very very useful and arguably necessary for a professional sounding piece.
High pass/Low pass filters: - a type of EQ that filters out certain frequencies. A low pass filter will filter out the high frequencies and let the LOW PASS through, so you hear only the bass frequencies.
You'll get the idea once you do a bit of research and testing.
IMO, the 3 most important things to have a handle on are EQ, Compression and Reverb (probably in that order) ...regardless if you're mixing tracks or mastering (arguably what you'd classify "cleaning up cassettes" as).
