I know how to sync my ipod, ipad and iphone with my imac but I don't know how to sync my mac air with my imac because my mac air does not have a place to stick in the cable that I use to sync the other apple products. Is there some mediating device I need? Thanks.
Assuming you're talking about the MacBook Air, you have to realize that Apple makes 2 products - computers and consumer portable devices. These devices are iPod, iPhone, and iPad. Their computers are virtually everything else you know, such as the iMac, Mac Mini, Mac Pro, MacBook, MacBook Pro and MacBook Air.
Their portable devices are made to work seamlessly by syncing to a host computer for all of their media. Their computers, however, are not made to sync with one another. It's like asking if you can sync a Dell to an HP. It just doesn't happen as simply as syncing a portable device.
Sure, there are programs and methods available to keep folders in sync with one another over a network, and sure, there are things like MobileMe that sync your calendar, contacts, and mail. However, totally syncing two computers is not something that is simple. At least not yet.
The next question is exactly what jdechko asked - what is it exactly you want synced?