Both a Micro training and an Assignment can ask participants to engage with content — but they're built for different jobs. A Micro training is for moving through content step by step. An Assignment is for having someone do something and hand it in.
Use a Micro training to teach
Reach for a Micro training when the goal is for participants to take something in: a series of slides with text, images, video, and optional questions to reflect on. The questions aren't graded and there's nothing to review afterwards — participants read, watch, answer for themselves, and move on. See Micro trainings.
Use an Assignment to collect work
Reach for an Assignment when participants should produce something and submit it — a written answer, a confirmation, a reflection that you or a manager will look at. An Assignment is the only activity type where a manager can be required to approve the submission before it counts as completed. See Assignments.
When you need the answer to be required
This is the distinction that trips people up. A Micro training's questions and text inputs are never required to continue — a participant can move past them without answering and still be marked complete. So if you need participants to actually submit an answer before the activity counts as done, use an Assignment. That's the type built to hold a required submission.