To take a bearing:
Line up the baseplate along the line of travel on the map (ie, lay it on the map and connect points A and B). Hold firmly in place.
Turn the circular housing until the big red arrow is parallel to the eastings on the map (the blue lines running N-S).
The bearing is the number at the white line on the top of the scale
To follow a bearing:
Hold the compass level and turn it until the red magnetic needle is lined up with the big red housing arrow. Walk in the direction of the baseplate arrow.
About as simple as I can manage…