The green Ability dice and yellow Proficiency dice both have successes and advantages on them, while the purple Difficulty dice and red Challenge dice both have failures and threats on them. Triumph and Despair are especially potent results that are only available on, respectively, the Proficiency and Challenge dice. The blue Boost dice and black Setback dice can add successes or failures, as well, but are more likely to add advantage or threat, respectively.
Also, the GM doesn't have to roll the negative dice. You can just tell the players what the difficulty is and let them do all the rolling, if you want.
I haven't had time to read in-depth on the Force rules yet, unfortunately. ^^; I know that you can roll light side dots or dark side dots on the Force die, and that you can activate your force powers by spending these dots, but I don't know too much beyond that.