It was an hour long interview process with one person over the phone. Questions asked ranged from finance questions to basic calculus questions. Other topics included basic option strategies and several mental math questions.
Phone interview was fairly typical of trading firms you can find all these online somewhere if you do your homework and such. Read up on probability and statistics and of course finance like options and derivatives
The first interview is a phone screen that's almost entirely technical. After that you are invited to actually interview. The phone interview is usually conducted by a junior trader or quant researcher