Having problems with Mail and a few other programs freezing I have a brand new macbook. I don't  really know a ton about macs...I'm newly switched from a life of windows pc's.  I keep reading about how you can unintall and then reinstall your OS. I can't get my head around how you would do this, bc w/windows you would have no way to get on the internet to access the program without an OS on the computer. I can imagine getting a drive to put it on, from which you could reinstall, but that seems to defeat the point if you think your version could be corrupt and want to ditch it and get a clean copy. 

My computer is the Macbook(not an air or pro), so it has no drives and only one port. I do not have any external drives.

When I bought this machine I asked the genius bar to transfer my files, music and photos only. They  ended up transferring my entire drive, which included windows folders.I've deleted most of this, but am not sure if I've removed everything and do not know if this could be the source of the problem. Could these files have corrupted anything?

Any thoughts greatly appreciated. Sorry if I appear ignorant! It's only bc I am when it comes to this :~)
First off, congratulations on upgrading to a Mac, I'm a Windows "switcher", too, and will never go back. Secondly, as far as reinstalling a fresh copy of OS X (pronounced oh-es-ten NOT oh-es-ex) you will want to turn your MacBook off, then turn it back on, but while holding the Option key. Release it when you see two icons of hard drives, whatever you named your startup disk ("Macintosh HD" by default) and one labeled Recovery. Select Recovery by highlighting it with the arrow keys, and then hitting the enter key. Once there, you should see the option to "Reinstall OS X" select it and just follow the on-screen instructions from there. Make sure to select your start up disk, again named "Macintosh HD" by default, where it asks which drive to reinstall it on.