If you're having trouble syncing your music, here a some things to check:
- On the summary tab of your iTunes sync settings you have checked "Sync only checked songs and videos"
- In your music library you have checked all the songs you want to sync to your phone
- There are no exclamation points next to any of the songs you want to sync to your phone
- You have authorized your computer for all Apple IDs for purchased music you want to sync to your phone (in Store>Authorize This Computer)
- You have checked "Sync Music" on the Music tab of your iTunes sync settings
When all these are correct your music should sync to youre phone.
Have you synced to your new MacBook before? If not, the first time you sync with a new computer iTunes will remove all iTunes media (apps, music, podcasts, etc.) from the phone and replace it with the media in the new iTunes library you are attempting to sync with. If your media has been transferred to the new library this isn't a problem, as it will simply be synced back to your phone when you sync. If not, you need to move your media to your new library, as well as other data you may be syncing with your computer such as photos synced from your computer to your phone, contacts and calendars, prior to syncing. Migrating this and other data from your pc to your mac can be accomplished using Migration Assistant, as explained in this article: http://support.apple.com/kb/HT2518.