As someone that may or may not have been involved in the burning of one of these places, I can tell you that's it's really not that hard.
Get some regular black electrical tape, pilfer your local bottle recycling bin and look for bottles that preferably have wide bases and high necks, but it's not that important.
Now, I'm not sure how old you are, so getting the gasoline might be hard without raising suspicions. On the other hand, if you've got a moped or something, it's not strange if you'd go to your local gas station and fill up an extra petrol can.
If you're a car owner or have a license, there is absolutely nothing weird about stopping, filling up the car, and filling up an extra petrol can. Just be aware that pretty much all stations, manned and unmanned, have video surveillance. The last thing you're going to want to do is to go to a petrol station in the middle of the night, dressed in black, filling up a petrol can the day before a burning.
The key to not arousing suspicion is and will always be acting like you know what you're doing, act like there's nothing wrong with what you're doing, and you have a right to do it. Therefore, get the gas in the middle of the day, with plenty of people around, say hi to the cashier if there is one, grab a cinnamon bun, and don't feel any compulsion to explain why you're doing whatever you're doing. Don't be that comedy movie character that tries to explain away why he's buying batteries, just because he's got a dildo or something.
At home, preferably in an open space outside, which can be hard if you live in an apartment complex, you fill up the bottle(s). There's no need to fill it *all* the way up, make sure the gas reaches the neck of the bottle, but does not fill up the neck completely.
Fair warning: depending on where you do this, the gasoline will smell *for days*. It's perfectly alright to do this in the basement of your apartment complex, especially if it's a really big one, but be aware that it will smell down there for days. If you do this, don't leave the evidence anywhere where it can be tied to you specifically, in case someone would (which is very unlikely) connect the sudden gasoline smell with a recent firebombing.
So whatever the fuck you do, don't do this in your fucking living room. Backyard or backyard shed or the balcony on free-standing house (not the balcony of your apartment!) is ideal.
Anyway, after filling up the bottles to about 80-90%, cut a rag or parts of a white sheet into long strips that you are certain is about 1.5x longer than the bottle(s). Make a good number of them, and then push them into the bottle(s) with a stick or sewing needle, since it can get fiddly. You'll want to almost plug the hole, so make it at least 4-5 or 6 strips minimum - even more, depending on what cloth you're using. You'll want them hanging off the side of the molotov, and reaching well and good into the gasoline in the bottle.
Regarding cloth, if you don't know where to get some good rags, both IKEA and Jysk have cheap bed-sheets, all-white, that people routinely buy just to rip up and use as cloths for cleaning windows, polishing shoes and whatnot. You'll get far, far, far more than you'll need for this just by buying 1 package.
You then tape it up real good with the electrical tape. You'll want to practically cover the end, to make sure that nothing actually spills. My recommendation is that you tape the end of the rags to the side of the bottle, so that the hanging rag basically folds back on itself, forming a hook or noose. This keeps the otherwise disparate pieces of cloth nicely together.
You then shake the bottle. The gasoline should very mildly seep out of the bottle and into the rag(s), making for easy ignition.
(I have to split this up)
