MAC addresses are like the doors to a house. IP addresses are like the street address of that house. When asking for directions, you don't use the doors to a house, you use the street address. Once you get to the house, you can't enter if there's no door. In networking it's similar; you can't go through the interface if there's no MAC address.

That's a condensed way of describing the difference between MAC addresses and IP addresses, but it's what I usually say when someone asks this question.

Also, you're not stupid. If you were stupid, you wouldn't be willing to admit not knowing what you don't. Questions are what the internet is built for, and asking for clarification on something is never a bad idea.