Well, it's an additional property that electrons (and other particles)
possess. Here's an analogy: think about the Earth
orbiting the sun--
Haven't you just been pounding into my head that electrons don't orbit
It's true, they don't--and yet that picture remains helpful and illuminating
in many contexts. So bear with me for a moment: think about the Earth. Not
only does it orbit around the sun once a year, it's also spinning once a day
on its own axis...
And that's what spin is! Although I suppose you're going to tell me that
electrons don't really spin, any more than they really orbit.
You catch on quickly. They don't spin--but it's tremendously useful to think
about them as if they did, and for most practical purposes, you can. In the
present case, think of the two electrons in that lowest energy level as
spinning in opposite directions. It's often said that one has "spin up" and
the other "spin down."
So each level has room for a spin up and a spin down--that makes sense. But
you haven't explained s, p, and d yet; there must be more complications to