How do I dock my blocks in Moodle?
You can dock blocks in Moodle to free up and expand space in the center column of your course page. Note that docking blocks is user specific; just because an instructor docks specific blocks does not mean the students in the course will have the same blocks docked. Once you’ve docked a block in a particular course, you won’t need to dock it again in that course. A block docked in one course is not automatically docked in a different course.
Link to this FAQ.