On a Mac, you can add metadata to your tracks using the iTunes application.
Step 1) Open your file using iTunes. (In iTunes, select File > Add File to Library..., then browse to your file.)
Step 2) Select the track, then choose File > Get Info.
Step 3) When the 'Summary' window pops up, click on the 'Info' tab at the top of this window. You should now see editable fields, where you can input your file's information. 
The fields of importance for Live365 are Name, Artists and Album. These fields correspond to the metadata fields in the Tracks section of Live365.
If you imported the file into your Live365 library without all the metadata, don't worry. You can also edit the metadata in the Live365 interface.
Also, be sure to check out this article on using MusicBrainz to find the correct track titles for your media library.