In trigonometry an angle is usually drawn in what is called the "standard position" as shown below.
In this position, the
vertex of the angle (B) is on the
of the x and y
axis. One side of the angle
is always fixed along the positive x-axis - that is, going to the right along the axis in the 3 o'clock direction (line BC).
This is called the
initial side of the angle.