We just learned about
And Or Logic Gates.
When we talk about letters and words, we know that
A is a letter,
and
Apple is a word with the letters A, p, p, l, e.
For numbers, instead of saying
letters we call them
digits
So the number 174 has the digits 1, 7, 4.
The numbers we use every day go from 0 to 9.
The
digits are: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
(The number 10 uses the
digits 1 and 0.)
Since there are ten
digits, we use the word
decimal.
What if we only had two
digits to use, 0 and 1?
Could we still make numbers?
Yes!
We can make the numbers: 0, 1, 10, 11, 100, 101, 110, 111 and so on!
Since we're only using 2
digits, we use the word
binary (like bicycle which has two wheels)
When we want to match up our
decimal numbers to our
binary numbers,
we just put them in the same order.
binary 0, 1, 10, 11 is the same as
decimal 0, 1, 2, 3
So b0 = d0, b1 = d1, b2 = d10, b3 = d11 and so on!
We already learned about how computers use
1 and 0
to turn lights on and off on your computer screen.
The whole computer uses just
binary numbers to do all the math to turn those switches on and off.
Just think, giving a computer a number like: 1110 can be like telling it to turn 3 lights on, and the other one off!

(from: wikipedia -
binary number)