Pooping and peeing are basic human functions. These are simple in a sticks and bricks house with indoor plumbing but take planning in a camper.
The simplest approach is to stay near places where toilet facilities are available. This might be in paid campsites, a friend's driveway, 24hr stores, fast food joints, rest areas, etc. Apps like Where is Public Toilet may help locate them.
Note that some free sites maintained by BLM, USFS, etc, have pit toilets onsite. These are outhouse-like structures. Bring your own toilet paper as there are no guarantees.
Read more info on toilets.