Kahoot! is one those tools that you can learn about today and use tomorrow...but if you need more help, click here a step-by-step guide. (I talked to a math teacher after school who already created one to use in class.) Teachers can use it for pre-assessments, during instruction, or at the end of a lesson to gauge understanding.
Here's an idea: Your students can also benefit from creating their own Kahoot!s as a means of review. Students who truly understand topics should be able to craft meaningful wrong answers, too. Further, Kahoot! creation can work well as a component to a research project. Students or groups could present information and then Kahoot! the class.