You are such a hoar…der. You can keep them on the MacBook Pro until you need them.
Or you could partition (fancy computer talk for “divide”) your 1TB drive into two 500GB partitions, and use 500 GB for Time Machine with your Air and 500 GB for files that you want to keep but don’t need on your Air.
You can transfer files directly from your MacBook Pro to your MacBook Air (or any other Mac) over Wi-Fi.
A “Solid State Drive” or “SSD” is a hard drive with no moving parts. You know those little memory cards they use in digital cameras (SD cards or CF cards)? They’re like that, only much larger. They’re really fast, and quiet, and run a lot cooler than regular hard drives, so the fans on the computer don’t have to run as often (or at all). The only problem is that they’re new and so they’re expensive compared to older drives.
Replacing your current MacBook Pro hard drive with an SSD is just as easy as replacing it with any other kind of hard drive. You just have to make sure you have the right kind of replacement drive. MacSales (aka OWC) has a good place to look for them, and obviously Amazon.
The exact “how to” depends on what model MacBook Pro you have, but there are instructions on www.ifixit.com for just about every model. It’s something you can probably do yourself, or you’ll need to find a local geek who can do it for you in exchange for monetary and/or sexual compensation.