Over is a preposition used in several different ways.
If one thing is over another thing, it is directly above it.
I had reached the little bridge over the stream.
His name is on the monument over the west door.
If you go over something, you cross it and get to the other side.
Sayeed climbed over the fence.
The sea was rough on the way back over the Channel.
If someone is over a particular age, they are older than that age.
She was well over fifty.
If something happens over a period of time, it happens during that time.
He'd had flu over Christmas.
There have been many changes over the last few years.
If you do something over a meal, you do it while you are eating the meal.
It's often easier to discuss difficult ideas over lunch.
➜ See above - over