List is a view builder. It's a factory.

For each and every item inside of a collection it will shove that item through some template and gronk out a single item to display on the screen.

So for every entree item inside a restaurant's menu collection, the List will spit out a single line formatted to your specifications.

For every team in a bowling league, the List will lay out the team's name and total score.

For each beer in a pub app, the List will show a frothy photo, and the price per pint.

The List command just takes the entire collection and builds a smaller view using the content of the objects in the collection, one at a time.

This is the same as the ForEach() function as well.

// This is a view factory! What kind of views is it going to make?
ForEach(0..<3) { number in
    Button {  //  <----- Here's the answer!  This ForEach factory will make Buttons! A valid type of view....
        flagTapped(number)
    } label: {
        Image(countries[number])
            .renderingMode(.original)
            .clipShape(Capsule())
            .shadow(radius: 50)
    }
}

user in? beer in?

In your code example, you wrote

// you're using the variable user to receive the object passed in by the List command
List(users, id:\.self, selection: $selection) { user in Text(user) }

// This may confuse you, if you also have a struct in your application named user.       
// Instead, you can call the receiver variable anything you want. Try this variation:
List(users, id:\.self, selection: $playerOne) { gamePlayer in Text(gamePlayer.avatarName) }

In this snip, you have a collection of users and you've coded user as the receiver's name. But in the List, you can call the receiver variable by any name you wish.

Keep Coding