The compass rose, also sometimes called the north arrow, is typically a spherical shape with four points emanating from it and spaced equally apart. The four points are usually labelled North, South, East and West, or N, S, E and W. The compass rose's function is to let you know which way north is on the map.
The bar scale, often labelled as the scale on the map, is the long thin bar with alternating black and white parts. The function of the bar scale is to let the map reader know how distances on the map relate to distances in the real world. For instance, if you measured the bar scale and found that one mile was equivalent to one inch on your ruler, and then you measured one inch between two features on the map, the distance between those two features in the real world would be one mile.
The Earth is round and three-dimensional, but a map is two-dimensional and cannot adequately represent a three-dimensional object such as the Earth. So the map must distort the surface of the Earth if it is to represent it. This distortion is called the map projection. For many purposes the map projection isn't important, but for navigating over long distances it is a critical piece of information in interpreting a map. If the map is sufficiently detailed you will often find information somewhere on it explaining the map projection.
The map legend is where you will find information on any other symbols that have been included on the map. Symbols for things like roads, railways, hiking paths, rest stops and bathrooms will all be explained on the legend by the mapmaker. The legend is typically located in the bottom left corner of the map.
