What you are referring to is swinging a compass: i.e., making sure that it is adjusted correctly and that North is 0, South is 180 degrees, and East / West are 90 and 270 degrees, so that when you are sailing a course, you are not off by 5 or 10 degrees due to compass error.

To do this - and you can find detailed descriptions of the procedure in almost any good sailing book - you swing the boat from heading to heading, pointing the bow at something that is a known North point; putting the stern to that point then gives you South: noting the headings; and then making the appropriate adjustments with the N/S or E/W adjusters - and use a BRASS screwdriver, otherwise if you use a steel screwdriver you are not getting correct readings..........