Step 2: Layering the batter

Get two spoons the same size, one for each color. Start in the center of the pan and add 2-4 spoonfuls of the first color. The more you use, the thicker your stripes will be. Just be consistent.
Take your next color and add the same amount of spoonfuls of batter, right to the center of the first puddle. Continue building, always from the very center. You'll notice the batter starts to spread towards the edges of the pan. Once my batter reaches the edges, I generally feel like I've used enough batter. You should end with a bullseye!
And seriously, don't try to spread the batter with your spoon EVER. It will end badly. You want to let gravity do the work. Once you get it all in there, you can pick up the pan and give it a nice thump on the counter to force it all to just settle a bit, but that's about it.

Extra batter is a total bonus. Make yourself a little snack.

Bake your cake according to directions. *Usually* about a half hour at 350 degrees, but check your box.