[otrs] Email tickets and how to get them together automatic

Hi, i'm new to OTRS and iv'e setup a test system based on incoming Help Desk emails. One feature i'd like to find a way to implement would be to group in a single ticket all related emails, meaning, one email opens one ticket and all replies to that email go to the same ticket. I've tried without success to find info on how to do this nad tried to figure out how could this be done but i guess i still have a lot to read about OTRS. Has anyone done this already, can someone help on this one ? Thanks -- Pete