Why "František"is in the begin of the sentence? Can I put it in the end of the sentence?
It's a way of emphasizing. When you put the name on first place you say that you definitely are not František. (And yes you can put it in the end. Nejsem František is a simple declaration of the fact that you are not František)
In long sentences is the word you want to emphasize mostly put on the end of the sentence.
That's true in general but this very sentence is really weird. I've never heard anything like this. It should definitely be "Nejsem František" in 99% situations.
I can imagine using this word order in something like:
František (sice) nejsem, ale (přesto)...
when somebody would expect me to be František in order to do something.
But imho there's no reason to put such delicate stuff here to confuse beginners.