You can craft a fishing rod here, which is an incredibly useful item to have. It allows you to cast your rod and catch fish when prompted. However, eating these raw fish is inefficient, and you can improve their hunger satisfaction by cooking them. To do so, you need to craft a grill. That is straightforward, and once you have it crafted you can place your fish upon it. However, you can't cook something with the power of sheer willpower alone, you need some fire. Placing planks upon the grill will allow it to cook. Give it time, and your fish will be cooked.