Inspect the water in the toilet bowl. If there isn't water in the bottom of the toilet, the problem could be as simple as toilet paper clogged in the blade. This means when you flush you let go of the handle too soon and the blade closes too fast, so the toilet paper gets pushed into the groove where the blade closes. Buy a tool to clean the groove at your hardware store if necessary. Use the tool to clear in between the groove. In the future, hold the handle down until the bowl is empty.
Replace the gaskets that can age over time. Remove the toilet to replace the gaskets, and replace the floor gasket to avoid future hassle.
Fill the tank with excess water if toilet paper is stuck high up in the toilet. This will get it wet and it will float, making it easier to flush.
Spray with a silicone lubricant if the flush mechanism is stiff. Also spray the blade and the gasket.
Inspect the water connection if leaking is the problem. If it is loose, tighten it with a wrench.
