What are ground tarps and footprints for?
In dry weather, ground tarps protect your tent from scratches, thus extending the life of your tent.
In rain, ground tarp is meant to prevent puddles inside your tent.
When rain is on the way, fold in the edges of the ground tarp to be under the tent. If the ground tarp sticks out, rain will seep underneath your tent and create condensation inside your tent floor.
A footprint is a ground tarp that is fitted to the exact size of your tent, so you don't have to fold in the edges.
Here's a video about what we mean by "fold in the edges"