The first step is to check the valve located behind the toilet to ensure that it is in the open position. If that is not the issue, you will need to shut off the water supply before removing the cap on top of the fill valve in the middle of the tank. Once you have removed the cap, you will need to turn on the water supply. Be sure to place a small bowl over the valve to redirect the water back into the tank. If water does not come out of the valve after removing all of the components, you most likely have a clog in the line leading to the fill valve.
To clear the line, you will need to turn the water off again so that you disconnect the supply line from the bottom of your toilet. While holding the end of the line over a bowl or bucket, turn on the water. If you still do not get water, you will need to shut off the water supply to the entire house. You may have a clog at the valve inlet, so you will need to remove the valve from the wall. If you still do not find the blockage, you will need to work your way back to the meter by removing sections of pipe until you find the blockage.