A collapse section hides some information until a person chooses to open it. It is like folding a paper note shut and opening it when you want to read what is inside.
For example, a help page might show each question as a heading. Selecting one heading reveals its answer; closing it hides the answer again. This can make a long page feel shorter when people only need a few details.
Use a clear heading that tells people what is inside, and show whether each section is open or closed. Keep important instructions visible when hiding them could cause someone to miss them.