My toilet is leaking from the bottome of the tank. Where do I start

Your toilet has a wax ring under the base. When the wax ring dries out it needs replacing. It sounds like yours needs that. It’s easy to do yourself if you are strong enough to lift the toilet up. Look it up on youtube so you can watch a video. Type in how to replace wax ring on toilet.

There.

I think Faye_beard means the tank holding water before it goes into the toilet. That has some metal bolts that can rust out, allowing the water to leak out. Turn off the water going into the tank, drain the tank by flushing one or two times, then check that the little hoses and nuts, the float, the chain, the arm, and the stopper are all connected and in good shape. Anything rusty needs to be replaced, including the big nuts and bolts. Dry the tank inside and out. Turn the water back on and add a few drops of blue or red food coloring to the water in the tank. As the tank is filling, you should be able to spot further leaks by the colored water. One or two flushes should be enough. Best wishes ☺️

I would try the new FLEX SEAL if you cannot or do not have the ability to change out tank. I assumed you meant where toilet joins to floor...but either way...Flex Seal ! Also comes in clear. and is made to work even under water !

If if is leaking from the bottom of the tank you can buy gaskets to replace. If it is leaking at the bottom of the bowl, it will need a new wax ring. I usually buy 2 because if you don't get it set right the first time you can't reuse it.

Take up and start with the wax ring w/ flange replacement, if problem still persist most likely there a crack in ceramic and you need to find where and then try flex seal clear. Next step is too totally replace.

I think Jewel is right. Here are some instructions on how to repair the leak.

http://cheapesthouseontheblock.com/how-to-fix-a-toilet-leaking-from-the-tank-bolts/