I'm slightly confused as to what you actually have, as apple does not make an iMac Air. Perhaps you have a MacBook Air, which in fact does have all the function keys like a windows keyboard does. If you look at the small row of keys at the top, they will have F1-F12 in the bottom right corner. To use them as the function keys, you may have to hold the fn button in the bottom left of your keyboard, then press them. Or there is also a setting in the keyboard part of system preferences that uses them as function keys primarily, and the screen brightness controls, volume controls, etc. must be used with the fn button.