First you need a character who wants something, even if (as Kurt Vonnegut said) it’s only a glass of water.
This simple dynamic is at the heart of ever plot. If you find plots difficult to write, this is where to start. Whether it’s wanting to stop the alien invasion or wanting the dog next door to shut up, as soon as a goal is identified you can start building a narrative.
You build this narrative by deciding what the character is going to do. You know what they want, so how are they going to get it?
The journey from not having what they want to having it, whether in a scene or a chapter or over the course of a novel will be what the reader follows and hopefully they’ll get into the momentum and flow of it.
But as well as providing a narrative, what the character does in pursuit of his goal also serves two very important additional roles.