Blackboard's "adaptive release" function allows instructors to set pre-conditions (or rules) students must meet before gaining access to content. These rules can include date, membership, grade or review status.
Navigate to the content item you wish to add the Adaptive Release rule to
Click on the contextual menu (down-facing chevron) and choose Adaptive Release from the drop down menu
A basic Adaptive Release rule allows you to set availability based on the following 4 criteria: date, membership in a group, grade, and review status. These criteria may be used singly or together.
Select a date and time for an item's availability to students (the same feature is available when you edit an item)
Select usernames or groups of students whom you wish to see certain content (Remember to click Go to pull up members of the course, if you use the browse menu)
Select a Gradebook Item, such as an exam. Then, select a condition for the item to be visible (i.e. if students received at least an 80% on Exam 1, the Word document will become available).
Select another item that you wish the students to mark as reviewed, prior to gaining access to this item
See Blackboard's own FAQ page on adding adaptive release rules.