Question about Air brushes

Hello there !! I am at a point where I would like to try an air brush but I don't really know much about that aspect of the paitning. How do you use it comapared to a classic brush and why ? Do you need special paints or the classic citadel ones I have work fine. In which case do you want to use it instead of the brush and vice versa. Lots of questions but as I get more comfortable with the hobby I just want to progress ^^ thanks !!