Q: i have download ios games bt how to install it on my ipad?

Downloaded them where, your computer's iTunes, iPhone ? You may be able to redownload them directly on your iPad via the Purchased tab in the App Store app on it.

Or you can sync them via your computer's iTunes (assuming that is where the apps are, if they are on your phone then you can copy them over by connecting your phone and doing File > Devices > Transfer Purchases) by connecting the iPad and selecting it on the left-hand sidebar of your computer's iTunes (option-command-S on a Mac, control-S on a PC will get the sidebra to show), and then on the right-hand side of the iTunes screen use the Apps tabe to select and sync those apps

Syncing apps from a PC : http://support.apple.com/kb/PH12315

Syncing apps from a Mac : http://support.apple.com/kb/PH12115