To define a list, give it a visibility, the readonly modifier, a type, and a name. The readonly modifier will be covered in depth in 2.4, but the importance of it is that it locks down the modification of the field. The 'type' in lists pertains to the kind of thing the List will be composed of. The type needs to be put inside the < > after accessing the List class.
When defining a list for the first time in a class you will get an error.
This is because we are trying to use something that is provided to us by the .NET framework, but VisualStudio doesn't know if we will or won't use it so it does not add it to their 'list of things you're using'.
What we need to do, then, is add a using statement. To do this, hover over the List class, click the lightbulb, and select using System.Collections.Generic. Once this is done the error will go away.
