The easiest option is to simply purchase an external USB DVD drive. Apple makes such a thing in the form of its $79 . Just jack it into your MacBook's USB port and shove your discs into it as needed. With it you can play DVD movies, play and rip CDs with iTunes, and install software if it's compatible with your Mac.

Of course Apple's isn't the only solution. Go to Amazon and search for and you'll find several external drives that are compatible with your Mac (and most costing quite a bit less than Apple's drive).

If you have access to another Mac that does have a media drive, your options expand a bit. In such a situation you can use the power of DVD or CD Sharing if you want to install software (other than the Mac OS) or copy files from a disc. It works like this:

To begin, your two Macs must be on the same local network. Now, on the Mac that has the media drive (ie. your MacBook Air), launch System Preferences, select Sharing, and in the Sharing window enable the DVD or CD Sharing option. By default the Ask Me Before Allowing Others To Use My DVD Drive option is enabled. Unless you're concerned about others on the network accessing discs in your Mac's media drive, leave this option on.