Design-batteryholder
Zooming in on the components of the first example http://interactionstation.wdka.hro.nl/wiki/Mona-lisa
The battery holder.
The battery is for providing energy to your circuit.
Your circuit "works", so it consumes energy.
The battery....it seems so simple, you buy a battery. But there are so many batteries, which battery to buy?
let's keep this simpel: for a circuit with LED's , the most simple circuits you need a "coin-cell" battery of 3V.
The LED asks for a voltage that is near this value. There are different LED's, every color has it's own Voltage value.
Now you could and should ask: What is Voltage?
And this is a question which is not so easy to answer! Voltage is quite a complex notion and it takes time to explain, and even then......for instance:
https://www.youtube.com/watch?v=zYS9kdS56l8
https://www.youtube.com/watch?v=zqGvUbvVQXg
https://www.youtube.com/watch?v=F_vLWkkOETI
So let's do this in the practical way: we need a battery plus holder for a LED, we take the coin cell battery and holder and it "works" because it has nearly the right values.
We can "get" this battery holder in Tinkercad: