Teachers insert ACTIVITIES into a Moodle course to cause the student to interact with the content, the course, and with other students.
Choices allow the teacher to ask a question and specifies a choice of multiple responses. It's basically a one-question survey/poll.
Try adding a CHOICE to your own Sandbox Course!
Forums provide the opportunity for asynchronous discussions.
Try creating a variety of different forums to see how each one is different.