"Electrons-in-boxes"

Orbitals can be represented as boxes with the electrons in them shown as arrows. Often an up-arrow and a down-arrow are used to show that the electrons are in some way different.

Beyond A'level:  The need to have all electrons in an atom different comes out of quantum theory. If they live in different orbitals, that's fine - but if they are both in the same orbital there has to be some subtle distinction between them. Quantum theory allocates them a property known as "spin" - which is what the arrows are intended to suggest.

A 1s orbital holding 2 electrons would be drawn as shown on the right, but it can be written even more quickly as 1s². This is read as "one s two" - not as "one s squared".

You mustn't confuse the two numbers in this notation