I am unsure how to explain thge difference but I can give you some examples. There will be times you can really use one or thge other but sometimes the two words can be interchanged.
I have gotten myself into a sticky situation with making two appointments for the same time and day.
The massive amount of snow made it a a difficult situation to maneuver in a small car.
The circumstances that made it hard to get to work can be helped by preparations to leave.
A struggling mother has some circumstances in which she will need help.
Example of interchangeability:
There are some situations/circumstances that can't be helped.
both used in one sentence:
The circumstances I have lived with have made it a sticky situation to get out of.