Hi Arielle
we don't know for sure how space was formed, but the best theory we
have, which agrees with all of our astronomical and physical
observations, is that space, and everything in existence in it suddenly
appeared in an explosion called the Big Bang, about 14 billion years
ago. What was there before? Well, no-one knows, and the theories
that try and discuss this are generally very mathematical, and hard for
everyday scientists like me to get to grips with. It might not even be
a question that we can answer properly using the science we currently
understand.
Space is not just empty. We know that space is filled with cold gas and
dust, but even if you were to take that away what would be left
is countless numbers of pairs of particles and anti-particles popping
into existence for a tiny fraction of a second and then disappearing
again! This is known as the 'quantum fluctuation of the vacuum'.
Space is way weirder than you ever thought possible.
Hope this helps with your question, or at least gives you more things to think about!
Lyndsay