Information in this memory can't be moved to the hard disk, so it must stay in RAM. The amount of Wired memory depends on the applications you are using.
This information is currently in memory, and has been recently used.
This information in memory is not actively being used, but was recently used.
For example, if you've been using Mail and then quit it, the RAM that Mail was using is marked as Inactive memory. This Inactive memory is available for use by another application, just like Free memory. However, if you open Mail before its Inactive memory is used by a different application, Mail will open quicker because its Inactive memory is converted to Active memory, instead of loading Mail from the slower hard disk.
This is the total amount of memory used.
I would download MenuMeters if you want to keep an eye on your RAM. When I first boot up my 11" Air I am only using about 600MB
Don't bother with any of the apps that are available either free or paid, they do nothing really. OSX will take care of the usage of memory. As the previous post explained you have to understand the way memory usage is displayed. If you are really out of RAM, OSX will page out to disk, it will slow things down but i doubt you'll notice much impact as it's paging out to your SSD rather than a spinning disk.
Unfortunately you can't add additional RAM to your MBA as it's soldered in. If you really are running out of RAM you have to accept any performance hit or buy another laptop with more RAM.
Wired means RAM that is permanently in use and cannot be freed.
Active means RAM that is temporarily in use and cannot be freed at the moment, but may be moved.
Inactive means RAM that is holding information for quick access, and can be freed or moved.
You don't have to free up RAM on the MBA. RAM is automatically managed by the system.
On Windows, it's slow to let the system automatically manage things because there are things that Windows do to ensure backward compatibility that makes it slow. The actual explanation is lengthy and confusing, so I'm shortening it for you.
But bottom line is that you don't have to worry about managing RAM under OSX.