first, graph the y intercept (red). This is the value of y when x is 0.
next, see if the slope is positive or negative. Positive means it goes upwards as x gets bigger, negative means it goes down. Since the slope is -2, it goes down.
Then, because it's negative 2, go down 2 and over 1 (blue). do this as many times as you like (you need only 2 points but more is a good way to double check)
Last thing is make a line that connects your points (yellow).