A DBQ is basically an essay. You are going to answer a question by forumlating an argument, developing a thesis, and supporting is evidence. The big difference between a traditional free response essay and a DBQ, however, is that the test writers have included a bunch of documents (usually 10-12) to help you. These documents could include letters, picutres, declarations, ads, maps, charts, tables, speeches, laws, court rulings. political cartoons, etc. Your job is to use BOTH the DOCUMENTS and YOUR OWN KNOWLEDGE OF THE SUBJECT as evidence to support your thesis.
The trickiest thing about a DBQ is that you really have to work through what each document can tell you about the topic. There is never just one way to interpret or use each peice of evidence. So you have to think about what each document is telling you and how it can be used to support your overall answer.
Here are several things that might help you out. Don't forget -- this is just a taste -- we WILL be working on this together during the school year!