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.
There are multiple ways to associate one record to another, including a custom-defined relationship that you can create using javascript. The simplest and most common way of relating two records though, we've already done. It's with a Reference field!
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 ...
