Do you have Excel?. It does a fine job with these things. But here's my Voyage 200 screen capture.
You're given a mess of x and y coordinates. Enter them in a calculator, Excel, whatever.
using your graphing calculator, at least a TI-83, go to the STAT button. Go to edit and you will see columns, for L1 enter your x-coordinates and for L2 enter your y-coordinates. That being done press the second button then the Y= button at the top. You need to press PLOT1 and make sure that it is on. For type, make sure it is a scatter plot. Then you can adjust your viewing window to see it. Now, to find an equation that is needed, go to STAT, scroll at the top to where it says CALC and pick QuadReg, that will give you an equation with the least regression