Imagine you have a big circle with a line going straight through the middle. You draw little dots on the circle all the way around, and then draw lines from each dot to the line in the middle. Some of the dots might be closer to the line than others, and the lines you draw from those dots would be more slanted than the ones from the dots farther away.
The Sokhotski-Plemelj theorem is like a magic trick that helps you figure out what happens when you do certain calculations with these lines. It tells you that if you add up all the slanted lines together, using a special way of adding that takes into account how close each dot is to the line, you will get a new line that is just as slanted but shifted a little bit to the left or right.
This is really useful in math because it helps you solve certain problems where you need to figure out what happens when you add up a bunch of things that are all a little bit different. The Sokhotski-Plemelj theorem tells you what the end result will be, even if it might seem really complicated at first!