http://www.vistawide.com/german/grammar/german_cases.htm Here is the link to a webpage that I used to teach myself the tricky "diese" rules. I hope it helps you!

dieser, diese , and dies are pronouns. We use them to point at sth. or some-one that is near by: Diese Frau ist schön. die Frau > feminine : die - diese Dieser Mann ist schön. der Mann > masculine: der - dieser Dieses Kind ist schön. das Kind > neuter: das - dieses OR: Dies Kind ist schön. das Kind > neuter: das - dieses OR dies

You really have to study these. They are determined by case and gender. I can't answer your question briefly.