First off it is free. You would download their server and install on the pic with your music files and install their client software on the unit you want to stream to. If you have s smart tv or smart bluray you can also install the client. Smartphones as well.
Are your computers near each other? If so, there are several ways you can do this. Window Homegroup being one of them. You can find more info from this article. Here.
Lots of ways. Look into DLNA. Personally, I have all my music, movies, and photos on a small NAS box under my desk. Anyone connected to the network can stream from this.