Most home toilets use the gravity flow from the pressure in the tank to create a siphon to empty the contents of the bowl. If the tank doesn't fill, then the toilet won't flush. The problem often takes just a few minutes to fix. You need pliers and a bucket.
Check the wall valve
Turn the wall valve to make sure it's in the on position. Listen for the water flow when you open the valve.
Check the fill valve
Open the tank and check the fill valve. Move the float up and down to ensure it isn't stuck. If the design of the fill valve allows disassembly, open it to clear any debris.
Check the water supply line
Turn the valve to the off position. Detach the supply line from under the tank. Use a bucket to catch any water that may spill from the tank. Direct the water supply line into the bucket and turn on the valve. Turn off the valve. This action sometimes clears debris caught in the supply line. If the flow from the supply line is low, there's a blockage in the plumbing and you need the help of a plumber. If the flow is acceptable in the line and reconnecting it doesn't cause the toilet to fill, replace the fill valve assembly.