English prepositions above, over and across.

Meaning "higher than".

Both above and over are used to mean physically higher than:

X
x

The water was over/above the wheels of the car.

There was a bright star over/above the city.

Note: if something is moving from one side to the other, we can use above or across:

.....X
x

A plane was flying over/above/across the lake.

When we want to say something completely covers another thing, we use over. They can be touching the thing below or not:

_________
x

When we painted the living-room, we put sheets over the furniture.

There were dark clouds over the sea.

Use over for quantities of things:

We counted over a hundred ducks on the lake.

There were over ten thousand people at the event.

But if we refer to a vertical scale: temperature or sea-level, we usually use above (the opposite of below):

It's only two degrees above zero today.

Seville is only seventeen metres above sea-level.

But it is common to generalize about the temperature by using over or above:

It must be over/above thirty degrees centigrade.

We use above to mean something higher up the page:

For a explanation, see above.

We use over to mean the next page:

For an illustration, see over.