A basic use of the compass is to assist in setting the map, which means aligning the map with features on the ground by turning the top of the map so it points north. It should then be easy to identify features on the ground on the map. If there are plenty of features around you that you can identify on the map you can set the map without using the compass. If you are not sure just which ridge on the map is the one you can see to your right or which of several pools the one in front of you might be then you need to use your compass.
First ensure that the housing is turned to a bearing of 0 degrees (due north) so that the orienting lines are parallel to the edges of the base plate and the orienting and direction of travel arrows are in line with each other. Then place the compass flat on the map with the sides parallel to the north-south grid lines and with north towards the top of the map. Next turn the map and compass together until the red end of the magnetic needle lines up with north on the dial. The map is now set and features on the ground should correspond with the map. If you are facing south the map will be upside down now but you should be able to identify the ridge and the pool. If the former is to your right, it should be to the right of your position on the map. If you are still not sure you can point the direction of travel arrow at the feature, turn the dial until the magnetic needle and the orienting arrow are aligned, and then read off the figure in line with the direction of travel arrow to get a bearing. Put the compass on the map and set the map. The same bearing on the map should point to the feature.