Randomly choose three values for "x". Substitute each of them separately into the formula to find the "y". Then write the solution as an ordered pair (x, y).
An easy way to find this is set you a definite y value. So try -3 as the value for y. Solve for x as normal so -3=-2x-1. Add 1 on both sides to get -2=-2x. Divide on both sides by -2 and get 1=x. Since the slope is -2 you keep subtracting -2 from -3 and you’ll get -5 when x=2 and so on.