Learning and experimentation is good, everyone started somewhere. There is a lot of information out there. If you are interested in the functionality of BackTrack then I would suggest hanging out in their community forums. They have a lot of tips and tricks. Just like with a carpenter, they have to know their tools and material. Be as it may - a hammer and wood respectively. If you want to be good at Red Team stuff, or infosec in general, you need to understand your tools and understand what you are attacking. You need to study up on networking in general and it sounds like wireless networking principles specifically.
1-can you attack an ftp server using backtrack? an email server?
Yes it has the tools to facilitate an attack against both of those types of targets
2-i have a centos vps and backtrack is on my pc, can i change the ip address of backtrack to my vps ip and do phishing using my vps ip?
A semi-complex question, the short answer is it is probably not going to work the way you've pictured it in your mind. Again you'll want to visit that networking stuff.
3-can i do brute force attack to crack email passwords using backtrack?
Yes there are a couple of different types of tools included that can help with this depending on your vector, generally the more access you have the more possible the chances are of a successful outcome.
All in all "there is no royal road to information security," you gotta put in the time and effort. All that technical stuff is one thing, remember to not forget about the weakest link in the entire chain are the people on the keyboards.