Minecraft wiki entry for Beginner%27s_guide, associated text: You can find apples and sweet berries which are immediately edible, but these are not very good food, and also don't warrant much further discussion. Grab them as you find them, eat them if you need to.
You can start a crude farm, which does not provide food immediately, but it pays off well later, as a head start toward a permanent food supply.
You can kill animals and cook their meat, to get some high-quality food for your first few days of the game.
You can kill spiders to get string, from which you can craft a fishing rod to catch fish, which you can cook for good food.