When you go camping, you probably want to bring at least a couple of tarps. Camping tarps are useful for a variety of purposes.
Use a waterproof tarp as a ground cloth, placed directly on the ground underneath the floor of your tent, to protect the tent floor from abrasions and tears from stones, pebbles, and twigs or roots on the ground. The ground cloth should be slightly smaller than the tent itself, to avoid having it collect rainwater to pool under the tent. If it rains during the night, the rainwater will run underneath the ground cloth, keeping it from getting the floor of your tent wet.
Some campers like to use a ground cloth inside the tent as well. A quality canvas or poly tarp of an appropriate size can be used as an inside ground cloth. This protects the interior floor of your tent, and it's easier to clean. It's also cheaper to replace than the entire tent.