Mark the point that will be the vertex of your angle.
Now line up the protractor so that the correct part is lined up with the vertex of your angle, and base line of the protractor us lined up with the line you already drew.
Now use the numbers on the protractor to make a mark on your paper that corresponds to the angle measure you wish to create. In this example the angle measure will be 50°.
Now use the straightedge of your protractor to connect the angle vertex to the new point you created!
Don’t forget to mark the angle measure so you don’t forget what it is.