How do I authorize my computer for Itunes?

For a Windows computer, see this instructions on how to authorize your computer

1. Open iTunes. At the top of the iTunes window, choose Account and make sure that you're signed in with your Apple ID.
2. Choose Account > Authorizations, then choose Authorize This Computer or Deauthorize This Computer.
3. Sign in with your Apple ID and password. Forgot your Apple ID?
4. Click Authorize or Deauthorize.

Learn what to do if iTunes keeps asking you to authorize your PC when you try to play purchased content.