c# - Why we should use IEnumerable instead of something else?

I have some rows of code:

public IEnumerable GetCardNames()
    {
        string[]cardname = new string[cards.Count]; 

        for (int i = 0; i < cards.Count; i++)
            cardname[i]=  cards[i].value + " of " + cards[i].suit + "\n";

        return cardname;
    }

What I confused about is why it's a better way to use:

public IEnumerable GetCardNames()

than :

public string[] GetCardNames()

or :

public List GetCardNames()

I have read a lot of answers about IEnumerable but I'm still not feel so clear about this one, I mean the benefit of using IEnumerable in this case.