We find a lot of problems with toilets. Always look at the base and see if the floor is discolored, this is often a sign of a leak at the wax ring. We frequently find that water has worked its way under flooring and will eventually cause damage to sub-floors and framing.
Check to see if your toilet is loose. We check for loose toilets be pushing them with our knee and see if there is movement of the bowl. All toilets must be bolted tightly down so there is no movement. A rocking toilet will cause the wax ring to loosen and will break the critical seal between the pipe and the base of the toilet. This brings up a important point, never flush anything hot down the drain, it can melt the wax ring and start leaking.
Modern installs have a flange on the pipe that holds the bolts. Often this flange will break and need to be replaced. They make a repair flange, don’t buy the cheap plastic flange repair kits, opt for the metal ones. Stainless steel screws should be used. Regular screws may rust off in a short time.
If your toilet runs, the flapper valve in the tank is likely leaking or the float is set at the wrong height sending water down the overflow. This can leak a lot of water and both repairs are very simple to do.
Another problem is the valve may be faulty. They are usually fairly easy to replace,