Related lists are powerful tools in ServiceNow, both for displaying data, and for doing work. They show up below a form, and can display any records you'd like, that are in some way associated to the one you're viewing in the form.
To understand how related lists work, you first must understand a key component of ServiceNow: Keys!
See what I did there?
In a database, it is important to be able to differentiate one record from another, with some key piece of information. This is ...