Glucose test??

Ok, where I'm from the doctors are all pretty stupid and really don't care about us patients. They never tell me anything and don't communicate or answer any of my questions!! I hate it but there really isn't anything I can do that I haven't tried already. Anyways, what the hell is a glucose test? When do I have to have it done? What do I do to prepare for it (if anything)? How is the test taken? Blood, urine, etc.. What should good results read? Bad? What other tests do they take from 25weeks and on?