Space is multi-dimensional, unlike the two-dimensional trees in the brand new district of Cambridge, UK known as Eddington.
Space is expanding because the universe is expanding.
It is expanding away from every point in itself equally like every point on the surface of an inflating balloon. It started at zero size and now it is about 30 billion light years across.
You are such a point. You are on that surface of the space balloon. It is where you are and moving makes no difference as wherever you go it is the same for you. You cannot be on a different place relative to the whole universe because you are in the universe.
Everything is getting further away from you in space.
Now what about time?
It is just another dimension. It is expanding. It started at no seconds and now it is about 15 billion years in duration.
Just as you are at the expanding edge of the universe on space (the point on the balloon that you cannot get off) so you are at the expanding edge of time. Look anywhere and you look back in time. The further away that star is, the longer it took for its light to reach you.
You can only look backwards in space and time. You must travel forwards as the edge of space time expands with you stuck on it. You cannot see the forwards (future) space time as it has not yet been created, you are stuck in the here and now, only able to look back and see and remember the past.
That is the arrow of time. Simple. Easy. A child of five with a toy balloon could get it. Nothing to see here, move along. Little joke there of course. God bless.