The difference is quite simple. The numbers you see beside each one is Linux kernel version. Fedora by default keeps three kernel versions (newest + two previous ones), and if newest kernel gives you some trouble, you can always boot into previous (presumable working) one. This has helped me several times.
The kernel is like the heart of your system, and it’s very important. I don’t think I can give simple and good enough description if you have absolutely no idea, what’s an OS’es kernel is. There’s definitely a wikipedia article and maybe some other good explanations in the net though.
So when you choose an older boot option, you boot with older kernel – but all the other updates you’ve installed are active and being used.
In general – when all works ok – you should use the latest kernel available to you, as kernel’s updates contain bugfixes and various other fixes, and even newer hardware support.
Hope this’ll help you to understand your system a little better. If explanation isn’t clear enough, ask, I’ll try to provide you with additional details.