It would appear that you have a blockage in your drain pipe system.
If you are on a septic system, make sure the tank is not over-full.

Calling a plumber would be the clean way to solve the problem, doing
it yourself will likely be dirty and stinky.

I'd try a plumbing tool called a "snake" first. There is a short
version designed for toilets that has a bend that fits into the toilet
trap which prevents scratching the porcelain. You rotate the snake as
you feed it into the toilet trap, and if you're lucky, the pointed end
of the snake will snag whatever is blocking the drain and you can pull
it out.

If that doesn't work, you'll have to start opening up cleanout
downline from the toilet. You can run in a full length snake into
each cleanout until the snake eventually snags the blockage.

Good luck.

Mr Fixit eh