Usually it isn’t necessary to backup you iPad manually but depending on your syncing settings and other situations, you might want to do it. Whatever your reason is, here’s how to do it.
First you should make sure that you have latest version of iTunes installed and if it isn’t, update it. Then connect iPad to your computer. Open iTunes and Control-click or right-click the name of your iPad listed under devices on the left side of iTunes. From the list choose “Back Up” and that’s it.