As with all DIY heaters like this, you need to be careful about carbon monoxide exposure and take precautions to not catch anything on fire. No brainer right? These aren't designed to heat your home, just a small area, enough so that you don't freeze or to heat water to sterilize it while camping or to cook with. There are many uses for it I'm sure.
Update: You do want to get the 90% rubbing alcohol concentration as opposed to the 70% if you can. I used the 70% for this as it was all I had at that time. Many swear by the yellow-bottled HEET as being the "best" in alcohol stoves, but I don't know if it is safe indoors. (?)
Light it on fire. The toilet paper itself won't burn much. I am very happy how well these work! No smoke (unlike the buddy burners that some say you can use for emergency heat in the house, but those put off smoke. I'll do a blog about those later.)
Anyway, burning it full out without the large can over it, it burned for a total of over 2-1/2 hours, getting lower and lower. You could control the heat and make it last longer with the larger can over it.
When you use the large can, you want to punch holes along the bottom edge of the can (which will be at the top when you turn it upside down over the smaller can). You can use a churchkey can opener (the ones that make a triangle hole). You want to, also, either punch holes along the other edge (that will be at the bottom when flipped over the small can) or make two vertical cuts to form a small door in a flap shape that you can raise and lower for more control of the flames. You could always cover some holes with tinfoil around the bottom to adjust the amount of oxygen it gets too. Less oxygen = less flame and less heat.
I let it cool off, put just a little more alcohol in it, and relit it for a short time, testing it....
"Frogs on a Raft" according to my friend Deb or "Toad in a Hole".