To expand on that answer a bit, the operation of Match on iOS devices is a little confusing. In spite of what Apple says, they don't "stream" songs the way a computer does. Rather, they download them and they remain on the device until space is needed. This little cloud/arrow symbol remains, but the song is on the device (that's the confusing part). So a lot of your music is already there and you'll be able to listen to it away from WiFi.
If you want to explicitely download songs to listen to offline, you can click the cloud arrow for individual songs, albums, artists, or playlists. The latter is a good way to download a lot of songs at once. You can create a playlist on a matched computer, it will appear on your iPad and you can scroll to the bottom and click "Download all".
To see what's on your device, go to Settings->Music and set "Show all music" to OFF.