The links provided above are great but if you want a tl;dr - for a new member like yourself there is not much difference, DT1 and DT2 members are users whose trust ratings are shown by default in  the "trust" section of user profiles. DT1 users are slightly more privileged in that they can kinda sorta elect DT2 members but eventually once you figure out whose judgement you trust, you should create your own trust list and at that point DT1/DT2 doesn't matter much to you.