hi how can i download rockstar games on my iMac . gta 5

FWIW, there is no Mac version of Grand Theft Auto 5 for Macs. You would have to purchase a copy of Windows and install it using Boot Camp. Then run the Windows version.

GTA V is not available for Mac as far as I know.

You can download GTA III, Vice City, and San Andreas from the Mac App Store though.

You should contact the developers and ask.