How does Napoleon in Animal Farm use propaganda, education, threats, and the animals' indifference to make himself powerful?
Napoleon, once he has established his position, does very little on a personal level to maintain it. Gaining power took a little doing, though, and he used the techniques you list to achieve his goal.
Propaganda - Squealer is the propaganda mouthpiece for Napoleon. Squealer is sent out primarily to convince the animals of two things: the animals are better off now than when Jones was in charge (which is, in general, not true); and if things change, Jones will come back. The former is just taking advantage of the basically unquestioning animals and re-writing history; the latter is using fear to maintain order. Both techniques work on this farm.
Education - The only animals who are offered an education are the pigs. Their ability to read and write places them in a position of superiority and authority over the rest of the animals. Even if they aren't right, the pigs are able to convince the other animals they are.
Threats - Napoleon figures out, early on, that indoctrinating the young is a good plan to maintain power (see education, above). He takes some puppies and creates for himself a personal guard and attack squad. When anyone needs to be reminded of who's boss (Boxer), the dogs growl. When a threat to their master's position is imminent, they chase or kill (Snowball and the massacre in chapter 7). This is also connected to the fear of Jones's return as presented by Squealer.
Animals' indifference - The animals are used to following others and doing what they're told. That's what animals do, after all. They aren't used to questioning or rebelling, and Napoleon knows it. He uses that against them, relying on their apathy to give him great leeway in his decision-making. When anyone questions him, Squealer starts his propaganda, the dogs growl, ...and the circle starts all over again.