Bootstrap collapsing data

Hello I am trying to figure how to do something similar to this page:
when it is in the mobile version. I want to click on a section, and for it to expand and show menu items. I’m not even sure what this would be called and what to search for. I am willing to use either bootstrap or normal html and css. Thank you for the help!

It is called a hamburger menu. Take a look here for inspiration.

Thank you very much!