The quadrilateral is on a graph and I don't know how to find the perimeter of it.
How do you find the perimeter of a quadrilateral?
Cornelia's suggestions give you some options to try, but here is another way of doing it. Since the quadrilateral graph is on the coordinate plane, you can use the distance formula to find the length of each side. For instance, if the quadrilateral is formed by points A, B, C, and D, you would find the length of AB, BC, CD, and DA by using distance = sqrt((X2-X1)^2 + (Y2-Y1)^2). X2 stands for the X coordinate from the second point, X1 stands for the X coordinate from the first point, Y2 stands for the Y coordinate from the second point, and Y1 stands for the Y coordinate from the first point. Think of X2-X1 as the number of spaces between the Xs and Y2-Y1 as the number of spaces between the Ys. The pythagorean theorem and the distance formula are actually the same thing so this is just another way of thinking about it. Once you find the four distances, you can add them together to get the perimeter.
The perimeter is found by adding the lengths of all 4 sides. Since your quadrilateral is on a graph, I assume you know the end points of each side? If the sides are all horizontal or vertical, then the lengths would be simply the difference between the x or y points (x for horizontal sides, y for vertical sides).
However, if your quadrilateral is "tilted" then you will have to create some right trianges and use the Pythagorean Theorum (a^2 + b^2 = c^2) to find the lengths.
I've given a general answer, but hopefully it is enough of a hint to get you going.