"le john" you have to hold the toilet flush lever down until the toilet flushes completely or else it stops. Or you hear the toilet randomly fill with water, then shut off, then fill again 15 minutes later. Now that's just annoying!
So how do you fix it? Well it usually involves the toilet flapper ball and a chain adjustment. I'll show you how to fix this one in the tutorial Adjusting a Toilet Flapper Ball - Flush Valve.
And for other common toilet problems see Troubleshooting Common Toilet Problems. From float balls to ballcocks to flush valves to chains and handles, I have you covered!