Syncing your iMac's iTunes content to your iPad is as simple as transferring files from any computer to an iPod. In fact, the procedure for doing so is exactly the same. If you find the process laborious and feel that it's not an experience you'd like to repeat having done it once, you'll be able to set your devices to sync automatically over the air, saving you the trouble in the future.
Download and install the latest version of iTunes on your iMac (see Resources). Using an older version of the software could cause compatibility problems.
Open iTunes, connect your iPad to your iMac using a USB cable and wait for iTunes to detect your tablet. Your iPad will appear in the left navigation bar of iTunes under "Devices." When it does, click on it.
Click on the "Summary" tab at the top of your iTunes window and then hit the "Sync" button in the bottom right-hand corner of your screen. Your iTunes content will then sync to your iPad. Do not disconnect your device until you see a message telling you it's safe to do so on your tablet.
Tick the "Sync with this iPad over Wi-Fi" box in the "Options" section of your "Summary" menu to sync your tablet with your iMac wirelessly. When your iPad is plugged into a power supply, iTunes will sync automatically if it's open on your iMac and your two devices are connected to the same Wi-Fi network.
You can sync your iTunes content on all your Apple devices via iCloud. Tap the "Settings" icon on your iPad's home screen, select "iCloud," and then enter your Apple ID. Select "iTunes and app stores" from your tablet's "Settings" menu, and turn on automatic downloads for content you want to sync.
Make sure your iPad is fully charged before attempting to sync your devices. Apple's tablets will not charge from standard USB ports on iMacs.