"In which one finds oneself" means "the situation that you are currently in" in a more complex but better-sounding way. So with the example sentence, you can also say "A situation is a set of circumstances 'in which you are currently in'," but it wouldn't sound as pleasant as using the expression "in which one finds himself,"...
another example might be: "I love to talk so I often find myself not listening to other people," which can also mean "I love to talk so I don't often listen to other people,". Both are grammatically-correct, but by using the expression "find oneself" it becomes more complex, advanced, and literary. I hope this helps!
For example, we can say "With rising interest rates, many people find themselves in a situation where they can't afford their mortgage payments anymore". Another way of saying this would be "With rising interest rates, many people are in a situation where they can't afford their mortgage payments anymore".
I hope it's clear. I can provide more explanations if it's not clear.