For all three of those, I'd suggest using YouTube to host the actual content. For temporary hosting of voicework, you could also use vocaroo. For songs and music, you might also post on bandcamp, but I'd suggest building up at least one full album worth of content before posting there.
For collaborations, depending on what you're doing, you'll probably find people anywhere from here to 4chan to spacebattles to fimfiction to conferences to real-life friends.
Once you've found people you want to collaborate with, you'll want to coordinate with them using a combination of a forum somewhere, private email, and some kind of real-time communication such as Hangouts or Skype. (Which you use depends on what your friends and collaborators use; if you end up with a choice, go with Hangouts.)