Good Day

I tried to understand the WaitForSeconds method trough the documentation and afterwards by looking here trough many questions but I still can't get it to work.

My setup is as follows:

  void FlipCardFaceUp(Card card_)
    {
       card_.isFaceUp = true;
       aCardsFlipped.Add(card_);
       if(aCardsFlipped.Count == 2)
       {
       playerCanClick = false;
       StartCoroutine(WaitASec(2));

       ((Card)aCardsFlipped[0]).isFaceUp = false;
       ((Card)aCardsFlipped[1]).isFaceUp = false;

       aCardsFlipped = new ArrayList();

       playerCanClick = true;
    }
}
IEnumerator WaitASec(float waitTime) {
    yield return new WaitForSeconds(waitTime);
   }

void OnGUI (){
       if(GUILayout.Button((Texture)Resources.Load(card.GetImage()), GUILayout.Width(cardW)))
         {
         FlipCardFaceUp(card);
         }
}

But It doesn't work, the game doesn't wait as if the function is not called. How exactly would I need to set it up so it will work?

If anyone can help me further with this I would appreciate it.