Draw a straight line down the paper.
Place the pointed tip of the compass on the line and rotate the compass around that center point, drawing a circle. (The circle can be of any size.) For clarity, label the points where the line and the circle intersect Point A and Point B.
Keeping the compass set to the same angle, place its tip on Point A with the drawing end of the compass on the edge of the circle. Turn the the compass to draw an arc between the edges of the circle.
Draw a straight line connecting the points where the arc intersects the circle.
Draw straight lines from the ends of the line you just drew to Point B, on the edge of the circle, to complete the triangle.