Siemen s7

Hi,
Like I am a not very experiend user from siemens s7 and there is so much lecture about it in pdf, can anyone tell me shortly what's the main difference between an FB and a FC. I will better mean: when to use an FB or when to use an FC ?
Thanks

Try THIS thread.

OK, I had to check a little bit better the existing threads....
Thanks and best regards for your link,
Markus