can you use your itunes on multiple computers?

if you log in with your apple ID on different itunes, yes. but after 5 different computers, you will need to deauthorize previous computers.

if you're trying to sync your phone to different computers, i would recommend not doing that, because apple devices only sync to 1 computer at a time.

You can have iTunes on multiple computers, however your library will be unique to each computer. You can use home sharing with iTunes to share music from one library to another within the same household.

Check out this support document http://support.apple.com/kb/HT3819