There are two places where you can find berries: tall grass and thin trees. While those trees are fairly easy to spot, tall grass is usually distinguishable by the yellow sprouts, so keep an eye for them. The simplest way to see if you've found tall grass or not is to see if the attack button symbol has changed to gathering symbol. Berries are a great food source early on in the game, which is why you should collect as many as you as soon as possible. Most of the animals in the game turn very slow, so use it during the fights. Simply strafe and they'll never catch you. Since stone and iron are two very important elements, especially early in the game, it's a good idea to build your base somewhere in the mountains where there's a lot of it. Every animal you kill will offer you some valuable resources, so don't shy away from it. Keep some spare meat around in case you feel like taming some of the beasts. It might cost a lot, but you get an extremely valuable ally.