How would you summarize the difference between direct and representative democracies?

In a direct democracy, people vote on policies directly such as the Brexit referendum where people got to directly influence the outcome of the result.

In a representative democracy people vote for representatives who present a particular plan, ideas and policies and ask people to vote for them. Whomever gets the majority vote has a mandate to carry out his policies. In this system the voter does not have direct control over the outcome.

Yes. I would advise you practice a bit each week. Even 30 minutes a week is good if you want to do well. The sat is timed based. The want to see how fast you can answer questions. So practicing a bit each week will help you.