partially obstructed drain or vent, improperly installed drain or vent
Inside the toilet tank there should be a small hose off of the fill valve that should be clipped to the inside of the fill tube to allow water to fill the bowl while it refills the tank after flushing.
That means that your toilet is clogged, or your toilet was clogged and you need to just flush once more.
look inside your tank and see that the toilet bowl fill tube is connected and flowing with water when flushed. the fill tube is a 1/4-3/8" tube that is connected to the fill valve to the overflow and it should be spraying water down the overflow when the fill valve is filling. or Call a plumber
A blocked drain.
Bowl fills up but doesn't go down? The toilet or the drain is probably plugged. Try using a plunger on it or fill a 5 gallon bucket with water and pour it into the bowl as fast as you can without causing the bowl to overflow. A lot of the time, this will flush out the line because that is 3 or 4 times the volume of water that is normally used.
You have problems in the tank. The flapper is not working properly and possibly the fill valve is getting old. Very easy to change both items in less than an hour, or hire a handyman to do it. Parts cost about 16-18 for a fill valve and 4-8 for a good flapper.
This is likely due to a slow leak in the tank. The water in the tank slowly seeps into the bowl, eventually causing the bowl to fill up. This could be caused by a worn flapper valve, a worn fill valve, or a cracked tank.
Most likely, the problem is in the cistern (the thing behind the toilet bowl with the handle in it). If you think it's obstructed, lift the lid on the cistern and see if you can see why; otherwise, fill a bucket with water and pour it quickly into the bowl. That flushes the toilet and will serve until you can get a plumber to deal with the cistern. It will also help to keep the risk of disease low.
the toilet bowl will fill the bowl to a specific level to allow the trap to work properly and once the tank is done filling then you should have no water running into the bowl. To test and see if your tank is leaking into your bowl just put a few drops of food coloring in your filled tank and if you see the color in your bowl then you most likely have a leaky flapper or flush valve or can be your height of your tank water is to high and its running through the overflow or the fill valve is syphoning.
You have to use toilet more
there can be many reasons and I will say my thoughts on just a few. 1. your toilet trap of the bowl is clogged with debris (toys, balls, etc) to fix = snake out toilet bowl or if necessary pull toilet bowl and snake backwards threw trap. 2. your tank flush flapper is closing to soon or your tank water level is not at right height to fix = change flapper or adjust water level height 3. your toilet arm before the vent is plugged because of back grade or debris clinging to the side of the drain pipe to test = pull toilet and run toilet water supply full on down threw toilet flange and see if any back flow. 4. your toilet main line is clogged from backgrade,roots,damaged pipe,etc but will let other fixtures slowly drain to test = camera toilet line from toilet flange out to street or septic or if no camera available then fill tub full and lav full and drain both at the same time and look at your lowest fixture trap to see if any back flow exists or open clean outs and if possible to see water flow .
Time to give up and call a plumber to clean your drain line.