If you haven't used Quizlet before, it's basically a database of questions and answers. I think it probably was originally designed for students learning a foreign language vocab but works just as well for keywords and short knowledge-based questions or facts. These are collated into 'sets', and these are great to have in your arsenal because you can make the sets you want once and then keep recycling them in lots of different formats. It's free for both students and teachers to make an account, although it's not essential for students to have their own account. You can upgrade to a premium account but I've never found I've needed to!
Remember that you don't have to make the sets yourself from scratch! It's usually quicker to search for an existing set and duplicate it. You can then add, delete or edit questions, add images or combine sets to make exactly what you want. I've put a video below explaining how to do this. I also show you how to change the format of the questions, print them and export them.
As I explain, I generally use two 'types' of sets. The first is just vocab, the second is all the essential knowledge from my No Gaps collections, a series of short, clear cut questions which I want students to be able to recall fluently. If you want somewhere to start for the former, I generally start with these sets and edit from there (some were created by a student and have some mistakes). I'm redoing all of the knowledge sets, but you can see an example here. The different types suit different activities.
Once you've got your sets, you have a load of activities at your fingertips, both within Quizlet itself (eg Quizlet Live) and by combining them with other tools. More on that over the next two posts!