Slope formula is y=mx+b. m is the slope and b is the y-intercept. You can plug the coordinates that are given, (-3,-3), to find the y-intercept.
y=-3/4x+b is the equation you have so far. Plug in (-3,-3):
-3=-3/4(-3)+b
Multiply -3/4*-3.
-3=9/4+b
Subtract 9/4 from both sides.
-21/4=b
Equation: y=-3/4x-21/4
-21/4 equals -5.25, so your y-intercept would be (0,-5.25). That is the first point that you can plot on your graph.
After this, to graph the rest of the equation, you need to use your slope, -3/4. Every point will be down 3, right 4 from the one before it. In this case, your next point to graph would be (4,-8.25). You can also find what the coordinates would be in the opposite direction by going up 3, and left 4 from the original y-intercept. In this case, the coordinates would be (-4, -2.25)
Graph the points: (0,-5.25), (4,-8.25), and (-4, -2.25). Connect all the points to form your line. Normally, graphing two or three points should be enough!
I hope this helps :)