Where can I get this from and where do I put it. I'm the tank or filter?
I didn't do this so this is all from reading not experience, but you should be able to buy it at a hardware store, cleaning supply place, etc. It's not really an aquarium product (though I guess a live fish store MIGHT carry it). Really cheap, you'll probably have to get at least a liter and then use only a tiny fraction of that.
But make sure it doesn't have other ingredients.
For a fish-in cycle, you are relying on fish excrement and decaying food, etc. to provide. For a fish-less cycle you need to do it yourself (well, I have read of people trying to use things like decaying food but that seems rather silly when ammonia is so readily available).
Note you need good media for the bacteria to grow on/in, which is usually the sponges and other non-carbon media in the filter. Carbon (if you use it at all, and you shouldn't need to during a fish-less cycle) is replaced, but the other media stays and holds the bacteria you grew. Very little of it is in the water, it is on stuff... so some is on rocks and sand (if you have any), etc., but in smaller tanks the key place is usually the filter.
Whatever you do, after it cycles, don't suddenly clean out all that ugly gunk and sterilize it.
If you are committed to fishless, be committed to patience while it goes on. It's really boring.
PS. I'd suggest a complete test kit, like the API Master Freshwater Test Kit. You want to test for ammonia to make sure you're keeping it just right, and after a bit start testing nitrites, then later nitrates. You should see nitrites start to rise, stay high for a while, then fall. As they start to fall the nitrates come up. eventually Ammonia disappears quickly (don't overdo dosing once you see nitrites, ammonia may drop rapidly after adding), and nitrites will also start to disappear quickly, and all that is left is nitrates. When that happens you are cycled.