Just a quick note: throughout this instructable I refer to myself as we. This isn't the royal we, I'm doing this project with a group of 3 other people for a class at UBC, so when I say we I mean us, my group.
Step 1: Set your X values
To demonstrate, we're going to use the equation y=2x3+6x2-12x+4. It's the same equation shown in the picture below, which looks a lot nicer. We chose this equation because finding it's derivative and antiderivative will be easy, so we can check our answer.
First, you want to put your x values down in your spreadsheet, I made mine go from -5 to 5. Also set your step size, I set mine at 0.1. You could also use 0.01 (it would be a bit more accurate) but you generally don't want to go smaller. Once your columns are more than a few thousand cells long, it takes forever for your computer to process them all at once. For my computer, below 1000 cells usually works well.
Put your step size in a cell (I use A2). Put your initial value at the top of the next column over, the second picture below shows you what this should look like. Then in the cell below (B2) type in "=B1+$A$2" without the quotation marks, hit enter. The dollar signs tell your spreadsheet program to reference A2 regardless of which cell you copy the equation into. Place your cursor over the bottom-right corner of the cell, there should be a small black square, click it and drag it down, as you drag it, you should see the numbers slowly getting bigger. It's hard to describe, look at the third picture. Drag this box down until you reach the other end of your X range, in this case 5.