How do I move the music from my iTunes library on my desktop computer to my iPad?

Connect the iPad to your computer and select it on the left-hand sidebar of your computer's iTunes (if you have iTunes 11 on your computer then you can enable the left-hand sidebar via control-S on a PC, option-command-S on a Mac), and then use the Music tab on the right-hand side of iTunes to select which of your iTunes music to sync to the iPad's Music app

Syncing music : http://support.apple.com/kb/HT1351

Thank you for your help, I have spend so much time trying to work it out, the old brain doesnt work so good these days. Simple when you know how!