Advertisement is, at its most basic, the idea that there are things you'd want to buy if you knew they existed. So they inform you these things exist. And you have seen (a few of) these ads before in your life. You love those ads, and you find them more entertaining sometimes than the media they were encapsulated in. Most people will use trailers before the movie as their example, and they tend to respond positively to those even after having seen them they decide they won't go to that movie. But I remember looking through the backs of magazines just to see what was sold, or looking through classified ads back when those were a thing.

Most "ads" aren't these kinds of ads though, and seek to manipulate you. They at least are just a grift, and only want to separate you from your money instead of, say, supporting a war that doesn't need to be fought.