Among the first rules you'll hear about writing is that every story must have a beginning, a middle, and an end. You can go a little more in-depth or into genre-specific element requisites, for example the "Refusal of the Call" in a hero's journey arc, but virtually every plot point can be sorted into one of the three key categories.
The exact shape and structure of your story depends on its genre and the age group it is intended for, but chances are it will follow the beginning-middle-end path.
The beginning is just that—the start of the story. It's here that you want to grip your reader's attention, introduce the protagonist, set the tone, and hint at the conflicts ahead. Eg. Katniss goes tends to her sister in District 12, hunts with Gale, and attends the Reaping Ceremony where she volunteers to take her sister's place in The Hunger Games.
The middle is the bulk of the plot. This is your character's journey, the changes they undergo over the course of their story. Most of the trials and tribulations occur here. Problems worsen and threats loom. Characters struggle and fail but persevere nonetheless. Everything culminates in the climax and falling action. Eg, Katniss is thrust into various Capitol fanfares and spectacles with the other Tributes and competes in the battle to the death.
The end is the resolution. This is where the story draws to a close. Loose threads are tied up—unless you're leaving a few open ends and hints at a sequel. It's the last impression you get to make on the reader. Katniss and Peeta threaten a double-suicide, are declared the victors of the Games, and return to District 12.
The beginning-middle-end structure is most often viewed from the perspective of writing a complete story, but what if it was broken down into smaller chunks?
Let's talk about treating your chapters like individual, tiny stories.
Regardless of their place within the larger beginning-middle-end structure, every chapter must serve a purpose. It can be major like the protagonist crossing the threshold and embarking on a quest, or something smaller like a run-in with their love interest that builds that relationship. The main thing is that some thing or another needs to be happening that effectively pushes the story that much closer to its end.
If a chapter is not a stepping stone for the character to cross the river that is your story, it will bog things down or put a damper on the story.
In other words, avoid doing what I did in the first draft of Bound to the Heart and devote an entire chapter to a character shaving in the morning and running errands in town. As much fun as that scene was to write, and as hard as it was to cut, it had no reason to be there because it ultimately served no purpose aside from a chance to show off his bare chest and serving as a guided tour of my research into ultimately-irrelevant-to-the-story Regency London hotspots.
But how does the beginning-middle-end structure apply to writing the chapters themselves?
Part of that has to do with cause and effect.
Stories often revolve around changes in your character's emotions and motives. At the beginning, they might feel downtrodden and desire the frequent creative writing class example of a glass of water. Stuff happens in the middle, the goal within reach but somehow always slipping out of their grasp. Finally, they get their glass of water and are satisfied.
This pattern can be shrunken down to the size of a single chapter.
The character is in one state emotionally and physically at the beginning of the chapter. Things happen to them, or actions are taken to bring them closer to their goal, and they end the chapter in a different state than they started. They could feel more determined after uncovering a clue pertaining to the mystery they are working to solve, frustrated by failure, shocked by a new revelation. Whatever the case may be, they have experienced a shift.
Though considerably smaller than an entire novel, the chapters building that narratives are often comparable in structure. There are times that this won't apply or that it won't work the exact same way as a beginning-middle-end. For example, the end of a chapter might leave a few breadcrumbs instead of wrapping everything up. A single chapter might be less about advancing the major plot and more focused on fleshing out a subplot. Slowing things down isn't all bad—provided there is reason to.
Remember that in writing chapters, as is the case with writing a full-length story, shifts need to be made. Whether that is a change in the character's emotional state or external like a circumstance affecting them or their relationship with another character, something needs to be different between the chapter's beginning and its ending.