Essentially and most simply put, plot is what the characters do to deal with the situation they are in. It is a logical sequence of events that grow from an initial incident that alters the status quo of the characters.
The use of a “clock” or “time lock” in your story can be very helpful when trying to work out plot issues.
The time lock is great help in focusing the actions of the Main Character, and can be as obvious as a meteor threatening to wipe out all life on earth in 48 hours, or the story taking place in the time it takes to make a pot of tea (3 minutes). The time lock forces your Main Character toward the point of climax; the Revelation. Otherwise, your story might go on forever. The Main character needs to make a decision or arrive at the place they have been moving toward before the clock runs out. You are giving the Main Character a limited amount of time to solve their problem, reach their heart’s desire, get what they want…win. By limiting their time you also force yourself to choose.
The alternative to the time-lock (clock) element of a story/plot is the “option lock”. By using an option lock your Main Character runs out of options in their pursuit of their goal, heart’s desire, need, etc. When your Main Character runs out of options, they must choose. Make their choice dramatic. Make it interesting: the difference between the worst of two evils; difference between two moral choices. or anything that drives the Main Character, even in this final moment to confront something they didn’t want to confront from the beginning.
These two ideas are not mutually exclusive. You can have elements of both the time-lock and the option-lock in a story. However, one or the other will take precedence.
Both these techniques focus your story on the final climax and give you a path way forward to follow in your story.
If you’re stuck in trying to figure out an ending…give the “time-lock” a try, and then continue to turn the Character in on their inner conflict as they approach the end.