First things first: Minimize flooding.
Shut the water supply off ASAP.
Take the lid off the toilet tank and close the flapper ASAP.
The flapper is that little rubbery thing with the chain that allows water to flow into the toilet bowl.The faster you can shut that thing, the less water you'll need to mop off the floor.
Now, to get that clog unclogged.
Make sure you're using the right kind of plunger.
And know the right way to use it.
There are loads of DIY plunger alternatives you probably have the supplies for already.
For deeper clogs, straighten out a wire coat hanger.
Or, get potion-y.
If all else fails, call your friendly neighborhood plumber.
No shame. 💩