Use must to emphasize that the user has no choice but to follow a specific course of action. Do not use must when you mean can.

Only use the word must when you need to emphasize the importance of a mandatory action. For example, if the action must be done in a specific way or at a specific time. If you overuse this word, it loses its meaning. Instead of using must, state the action in the imperative form. You can use the imperative form in procedures or conceptual information.