It may be desirable to check that learners have demonstrated mastery of an activity before permitting them to proceed to subsequent activities. The option of mandating sequential learning is supported by enabling Require users to take activities in sequence on the course. Go to course > details > check Require users to take activities in sequence.
Once enabled, learners can only proceed to a subsequent activity when they have mastered the previous activity. Note how the links to subsequent activities in the course navigation are inactive.