>>1309990get a new chain man. Any KMC 8 speed. Those are easier to change than shimano ones. You need a chain tool as well, to shorten it and to break the old chain.
It's only going to be like $15 for the chain, and $15 for the tool if you buy them online.
While you do it, get some kerosene, and a tub of grease (any grease, wheel bearing is fine, from an autoparts store, or specific bike grease like park or phil if you want it). Once your chain is off, take the cage of your rear derailer off with an allen key. Keep a note of which jockey wheel went where (they aren't the same). Clean all the parts them in a little container with kerosene and a toothbrush. Then dry them with a rag and time, put a tiny dab of grease on the inside parts and re-assemble. It's really easy. You just take the cage bit apart, leave the body of the derailer.
Also clean your cassette the best you can. I doubt you have to replace it. If you want opinions on wear, post a photo of it. It's not expensive or hard to change that either if you just wanted to. 8 speed parts are cheap.
While your chain is off (or just lift it off the cog), spin your crank, and if that's rough, change your bottom bracket. That's not hard or expensive either.
And spin your wheel hubs. If they're rough, I'd get a shop to service those, the adjustment is a little tricky. But that won't cost much either, probably $20 a wheel or so.
DEFINATELY do these things, even if you intend to sell or upgrade. You'll learn valuable skills, you'll get your money back if you want to sell, and you're helping not contribute to our throwaway culture. And your bike will ride a lot better.
