Hi there, KawallPotato! :)
Finding the slope of a line is finding the rise over run, or the change in y over the change in x. Let me show you what I mean.
Slope = change in y / change in x
Or in other words,

Let's try it with AB. The first thing to consider is the placement of the letters. The blank space is asking for the slope of point A to point B, which means that the coordinates of A are your y₁ and x₁ values and the coordinates of B are your y₂ and x₂ values.
Put them in the equation like this:

2 - (-1) is a double negative, so it becomes 2 + 1, which is 3.
-1 - (-4) turns into -1 + 4 for the same reason. The change in x is also 3.
, so the slope of line AB is 1.
Using the same method, we can solve the next three problems.
Coordinates of B: (-1, 2)
Coordinates of C: (5, 1)
Slope:

The slope of BC is -1/6.
Coordinates of C: (5, 1)
Coordinates of D: (1, -3)
Slope:
, so the slope is 1.
Coordinates of A: (-4, -1)
Coordinates of D: (1, -3)
Slope:

The slope is
.
Quadrilateral
is not a parallelogram because it has only one pair of parallel opposite sides.
I hope this was helpful. Have a great day. :D