How do you save data when the iphone app goes to background or foreground state?

I have an app where the users enters certain information. Each time the user wants to, he adds a new item to a table list. When the user is done, they click the finalize button to finish the list and they can start another list.

In the AppDelegate.swift file, I see a few preexisting functions. applicationDidEnterBackground says to save information before the application enters the background (I'm assuming it's when the user presses the home button while using the app...).

In my app, each time the user adds items to the list, then goes to home screen and locks the phone, after a while the items are gone. So the information they added don't save. I'm thinking to use the functions in AppDelegate.swift to save information and load information each time the app is minimized or maximized. My question is, what is the best way to save this information? Would I just write to a file and read from a file or is there a way to automatically save and load this information? I've read something about saving objects to a .plist but I don't necessarily know how it works since when I click the info.plist it just takes me to table of settings and no code.

Thank you in advance for the help!