Well, I'll take these questions one-by-one, although the last is extremely vague.
Fedora is not the same as Redhat. Redhat is a company. They produced Redhat (the Linux distribution), which is no longer being produced. They now produce, and actively support Redhat Enterprise Linux, their "enterprise" version of Redhat.
Fedora is a spin-off project started and unofficially supported by RedHat.
Now, to your next questions, which are basically one in the same:
Redhat and Debian are Linux distributions
FreeBSD is a BSD Unix distribution
You will get so many opinionated reponses on "which one is better?" Trust me -- asking that will not help you. Each has their advantages:
Redhat is corporate, so if you buy their product, it comes with some official support, and you can buy more of it.
Debian (in my opinion) is a very powerful Linux distribution, and my Linux of choice -- very versitile, with a strong community backing.
FreeBSD is not a Linux, it's a BSD Unix -- quite a bit different. FreeBSD has claimed it's stake in servers, due to its long-standing reputation as being very stable and secure.