You have to collect food (fish and berries) by driving into ponds/bushes. Then when the fish/berries is in your car, drag them over to envirobear's mouth and he will eat them. When you have enough, a message will pop up telling you to hibernate, which means that you have to drive into the nearest cave.
Remember, envirobear only has one paw, so you can't accelerate and steer at the same time.
Also if your car gets too full of fish, rocks, leaves, badgers etc you can throw stuff out of the sun-roof by dragging it towards the top of the screen.