Repair most toilet leaks by purchasing a toilet repair kit and replacing the parts where the leaks occur. The kit is less than $20 as of 2015 and is less expensive than buying parts individually. It also helps to prevent numerous trips to the hardware store.
Some toilet leaks occur inside the toilet and do not leave water on the floor. Hissing sounds within the toilet indicate a ballcock valve that is not closing. The excess water leaks through the overflow tube and down the drain. Replace the valve and adjust the water level so it is below the overflow. If the flapper valve is not closing correctly, the toilet starts to run every 20 to 30 minutes for a few seconds. Use the replacement flapper to fix the leak.
Leaks from the bottom of the tank could be coming from the supply line attachment of the attachment of the tank to the bowl. Tighten the supply line where it attaches to the tank. If it continues to leak, replace it with a stainless steel braided supply line. Rusted bolts or worn gaskets where the tank and bowl attach are common sources of leaks in older toilets. Remove the old bolts and lift the tank off the bowl. Replace the large washer where the two connect, the bolt washers and the washers.
Fix water leaks at the floor level by turning the bolts one turn each. If the toilet continues to leak, replace the wax ring.