Ooh boy.
So the affinities are generally pretty playable if setup right. Sounds like you got a deal,so I'd recommend taking it to a shop and having them re string it, clean it up, polish the frets, and lower the action as low as it will go without buzzing. I'd tell them to restoring it with the lightest gauge strings they have. Light strings and low actions make for less sore fingers. If you're handy, you can do all that yourself, but it's easiest to just let a shop do it if they'll do it for under a hundred bucks.
If you don't have one, get a chromatic tuner with a metronome. $20 for a basic Korg model and it'll be the best money you ever spend, next to getting the guitar setup.
There's a fella on YouTube that is a one-stop-shop for quality guitar lessons, Justin Sandercoe. He's got everything from level 0 to pretty advanced stuff. He has riff and licks lessons, song lessons, and all the usual stuff, but he also emphasizes music theory and ear training, which you absolutely need to embrace sooner rather than later.
As far as the amp, it should have a "gain" setting. That's the crunchy, oozy goodness dial that makes those little power chords sound like the hammer of the gods or a rollin freight train. Reverb is the dial that makes it sound like you're playing in a big ole empty concert hall. Or a bathroom, if it's a cheap amp like thst one.
Your guitar is a single coil guitar. It will never sound as fat and full as a humbucker coil guitar, and it will not handle gain as well. Moving away from the amp will reduce the harmonic feedback you're getting, as will playing with the 5 way switch thst selects which pickup(s) youre using. Positions 4 and 2 are the ones that pair pickups (i think, it's been a while) and should reduce feedback. You'll notice if you hit the switch all the way in one direction it will sound brighter, harsher, and more aggressive. That's the pickup nearest the bridge. Push it all the way the other way and it'll sound more mellow, that's the neck pickup. If ya wanna get down and boogie, you need a little gain, a little reverb, that gnarly bridge pickup, and a shuffle groove.