A 45-degree angle looks like the bisection of a right angle. If one constructs a right angle by drawing one axis horizontally and the other axis vertically, a 45-degree angle is halfway between a flat slope and a vertical slope.
One way to create a 45-degree angle is to start with a straight line, then use a compass to create a perpendicular bisection, then finally create a bisection of the first straight line and the perpendicular bisection.
It is also possible to draw a 45-degree angle without a compass by using graph paper. Because a 45-degree angle has a slope of 1, one can create the angle by plotting points (x,y) starting from the origin (0,0) where x and y are the same value. For example, by plotting points (0,0), (1,1), (2,2) and so forth, and then drawing a straight line between these points, the line creates a 45-degree angle upward from the x-axis.