Last.fm is a platform that enables you to "scrobble" (as in listening to a song) and save amounts of times you have listened to specific artists. It can track your taste from Youtube, Soundcloud, AppleMusic, Spotify, etc.... The platform is very good for finding artists that you may like and it can help in finding hidden gems. Everybody on the platform has a profile and is able to look at statistics like for example how many times they have listened to an specific artist.
Bandcamp is a known platform for releasing music, buying digital releases from artists and buying merch from artists in general. Its a great source, if youre willing to spend a bit of money on digital albums, even tho a ton of great projects are downloadable for free on BC. Oftentimes huge discographies with tons of really good albums are very cheap and you can buy those for very cheap and get 10-200 Releases that you can download in whatever quality you choose to (from .mp3 low qual, to high qual .flac and .wav files.). The platform is also very good for finding old and rare releases from artists and you may stumble upon some cool hidden gems.
Soundcloud is a good, free streaming service that lets you also cache music files so you can listen to them without internet. A ton of young, upcoming artists use this platform to share their music, because the platform is very easy to use and the underground scene is very popular. Also a great platform for stumbling upon young talents that deserve more attention and it is a place for some of the most underrated, goated hiphop artists that never made it into the light of the mainstream. Theres also a paid-for version that enables you to download music, avoid advertisements and gives you access to music that is locked behind a pay-wall.
Spotify is likely the best paid streaming service for music that exists right now, even tho soundclouds paid-service competes with spotify very well, spotify has way more music and a local-file system. Finding music is pretty easy, since a lot of playlists (official and user-made) exist for literally anything. The official playlists are often kinda bad, but they can help some people get into genres that they havent gotten into. The non-premium version of spotify is very bad and absolutely not recommendable, soundcloud easily tops free spotify. Local-files in spotify are kinda difficult to figure out, but when you got it working, its pretty simple to use.
Quick Tutorial (premium needed):
You have to be logged into spotify with the same account on PC and phone and both devices need to be on the same Wifi (LAN doesnt work).
On PC, you go into Settings > then scroll down to "Library" and turn on "Show Local Files".
Then there should be the "Show songs from" option, I advice you turn off "Downloads" and "Music Library", create a new folder on your PC where you only add your music into and then link it with "Add a source".
After that add any mp3 files into the folder and they should appear in your "Local Files" playlist that is automatically created. Add the files into any playlist of your choice, because the Local Files playlist doesnt sync with your phone. You have to download the playlist on your phone and it should automatically download the local-files on your phone. (important!: make sure you edit the artist and song information however you want them before you add them to spotify, cuz spotify is dumb and doesnt let you edit the file after you added it into the local-files folder.)
Be careful when you delete the playlist, the files get lost on your phone and you have to add them into another playlist and then download that playlist to get them on your phone again.
As Youtube provides visuals to any audio, it can be used to enhance and visualize what the artist intends to show with the music. Theres some good channels that upload mixes of different types of music, which may show you some artists that you dont know. As youtube has its many videos, theres a great chance of you finding old music that is practically impossible to find nowadays. I dont have a clear opinion on YT Music, since I havent used its paid version, but to me it seemed like it kinda sucked, since Spotify is way better established and YT Music doesnt really have any own Pros. Also I've heard of some cases where whole playlists got deleted for "Hate Speech", which does not make any sense since the playlist shouldnt have anything to do with videos in it, but its whatever.
Whetever you choose to use Itunes/Apple Music is up to you, but to me its also easily replaceable with Spotify, especially with the fact that a ton of music is lacking, a lot of albums are "tagged" wrong (f.e. if the bands name is "ミドリ", it will get written out like "Midori". This counts for band-names, song-names and album-names that all get autotranslated. Also if you use last.fm, everything that is usually spelled out in another language is then autotranslated into latin-letters and it will mess up your scrobbles).
This platform is very known to have an terrible community, nevertheless im listing it here, because its still a great way of finding amazing projects. As the name indicates, you can rate music, I personally use the site mostly just for looking through genres and release-years to check if theres some good releases that I have missed and not listened to.