Serialized Array: Trying to wrap my head around it

So I am trying a serialized array used for selecting weapons. What's the proper way to call or set that info from a method?

I've seen it working with a "for" loop and an "if (Input.GetKeyDown)" - but I'd like to change weapons based on collision, and am hoping to do that via subclass & overriding on a separate object you collide with.

     public GunDefinition[] guns;
     public int selectedGun;
 
         [System.Serializable]
             public class GunDefinition
             {
                 public GunLauncher launcher;
             }
 
             public virtual void GunChooser (){
                 for (int i = 0; i < guns.Length; i++) {
                 // this doesn't work
                 selectedGun = 1;
                 }
             }