The Porta 02 is a basic starter or scratchpad recorder.
It runs at "normal" speed and has no noise reduction. It will record up to 2-tracks simultaneously. The mixer section is a playback side & cue monitor mix only with just Gain/Pan knobs. There's no extra features like EQ or Aux-Sends in the mixer section. There is no mixer function on the input-side of the unit, at all. It's just Input 1 and 2, straight in. Each input will acommodate either mic or line/instrument signals on 1/4" jacks. The Porta 02mkII has a dedicated guitar input on 1/4" jack, which is a handy little feature, but not a deal breaker if you don't have the mkII.
The fidelity on the Porta02 is decent, for what it its. Just try to keep your inputs/track levels running about 0vu average w/no more than +6vu peaks, and you should be fine.
We speak of the Porta 02 as a low end starter system, and it is that, but if I had something along the lines of the Porta 02 back when I started (with tape-to-tape cassette overdubs), I'd have been ecstatic at the high tech wonder of the Porta 02.
In these days of post-2k technology, the Porta 02 is not very high on the recording food chain, but despite all my other huge systems and rows of high end Porta's, I have a Porta 02 in the line up, and for what it is, I think it's a fine little machine. I have one, and that's the best endorsement I can give it.
To migrate your 4-track tape mixes to the 'puter, you'd typically connect from the Porta 02's line out to the 'puter soundcard's line in, using an RCA-to-1/8" stereo Y-cable adapter. You'll also need recording software and cd authoring software.