The water in my toilet water tank won't stop running What is the problem

The flapper or the ballcock is not closing properly. Is the flapper shut. Turn off the stop valve to shut off the water.

If your tank is not over flowing I agree with ma 100%, you have a bad flapper. Flappers wear out, rims get pitted and sometimes the flapper comes unhinged. I'd wiggle the flapper into place and see if the tank fills and shuts off. If that works replace the flapper for about $3 but check the rim it seats itself on, make sure its smooth.