Sync with iTunes.
Connect the iPad to the Mac and launch iTunes.
Click on the iPad name on the left side under devices.
Click on the Music Tab on the right.
Click on all of the albums or playlists that you want to sync - or the entire library if you like.
Click on the Sync Music Heading.
Click on Apply in the lower right corner of iTunes
Do the same thing in the photos tab under the Sync Photos From heading.
If you are using iTunes 11 - from the iTunes menu at the top - go to View>Show Sidebar so that you can see the devices heading on the left.