How do you connect my LG pop to music on my mac computer?

You are likely to have to put the music on the phone manually.

If the music you want to put on to your GD510 is in iTunes then open your home folder/Music/Itunes/Music and then you should be able to Copy + Paste your tunes onto your phone or phone memory card. Just remember .mp3 is the best format for the LG pop. Believe me this gets quite annoying after a while!