How are the career tributes different from the others?

I am assuming you mean in Suzanne Collins' 'Hunger Games' series. The career tributes trained for the Games for their whole lives, and learnt how to handle weaponry and self defense items (e.g shields) from a very young age. They have always been well fed and are in peak physical form. The other tributes are generally from poorer districts so they may be slightly (or significantly, depending on their district and their status within the district) malnourished. They will not have learnt how to handle weapons solely for the purpose of the Games, if they are able to use one fluently then that is pure coincidence.

Most importantly, from Katniss' viewpoint, the career tributes, having always had enough to eat, do not know how to go hungry. Regular tributes almost always do, therefore they are able to survive for longer on less.