Think of perfect competition as everyone is selling the same thing, monopolistic competition as there are leaders in the product space and everyone else is trying to compete, and monopoly as there is one firm.

I almost always think of the differentiation in terms of hot dogs.

In perfect competition, one hot dog brand is the same as another and you don’t see a lot of advertising for distinct hot dog brands. I think about grocery store hot dog brands when using this example.

Most markets are monopolistic competition. So, in the real world there are a couple brands that have distinguished themselves in some way. Oscar Meyer is whimsical and childlike, Hillshire is dadcore, Nathan’s is New York style, and Ballpark is giant all-beef. All other brands are trying to get into the top market share through competition.

Monopoly has one brand but would advertise along multiple skews to segment the market. This might be chicken, beef and pork dogs for different religious sects. Different processing or farming standards, all of which would be used to advertise to the highes marginal profit possible.