Rear end, tires do not turn when the transmission is shifted into drive or reverse?

Okay, I would first raise the car up in the rear on level ground, here is a guide to help:

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

With the parking brake off and the transmission in neutral you should be able to spin the driveshaft, this will tell us if it is the transmission or differential is having the issue. If it spins, lower the vehicle and check the transmission fluid level.

This guide can help you with that as well:

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

Please upload pictures or videos in your response of any problems so I can see.