Numbers & XYZ’s

In Yu Gi Oh there are cards called number or XYZ cards, these cards a rarer and harder to summon. (See the link on Yu Gi Oh Home) I suggest you read the list below which shows the differences with numbers…

1. Numbers can only be destroyed by other numbers or trap & spell cards.
2. Numbers need some special cards to summon them (See the picture of Number 39 Utopia Roots)
3. The cards used to summon numbers are not put in the graveyard instead kept underneath the number in whats called an overlay network.
4. These cards are called XYZ materials. I know this sounds confusing but it is easy to learn once you get used to it.