Click on the play button (middle) and on the next screen, click on the box marked 1 to start from the first level.
Your goal is to get all the acorns in the level peeled. You can do so by dropping heavy objects on them. You'll notice that some items are made of wood. These can be chewed by the Chip family. Your job is to decide where to place the chipmunks. You can only put one chipmunk on one wooden item at a time, so you must put them all in the right places.
Once you've placed them where you think the wood they will chew will cause a collapse that will peel the acorns, click on the yellow button that will appear on the left side of the screen.