tldr: for me it's $4.99 a month + tax and if you're a student it's 50% off. have access to most songs you'd find on spotify + fun remixes.
SoundCloud is kind of a social media thing where you can follow friends and musicians. They let you comment on songs and sometimes the musicians will write back to you! If you find your favorite musicians, you can do a radio station based off of them and it's pretty good most of the time. They create a "Mixed for you" + "More of what you like" playlist daily and a weekly roundup.
But in addition to most of the songs you'll find on Spotify, you'll find independent musicians doing their own thing like on old myspace. SoundCloud's also good for hosting tracks that don't pass copyright laws (i think) so there's a lot of unofficial mixes and takes. There are podcasts too.
As a musician, I'm not very good at posting my stuff and sharing it around, I still use Bandcamp as lucius recommended, I like that a lot. So I'm not sure how other artists feel about SoundCloud.
Anyhow, it's $4.99 a month if you don't want ads and want access to all music.