Quick answer
a ver
Natural: let’s see / hang on
Literal: “to see”
How it is used
A ver, déjame pensar.Let’s see, let me think.
A ver si funciona.Let’s see if it works.
¡A ver! Escúchame.Hey! Listen to me.
A ver qué dice.Let’s see what he says.
Where it is said
It is universal, though in Spain a sharp <b>a ver</b> can also be a mild “come on now” when someone is being unreasonable.
A mini dialogue
— ¿Puedes abrir el archivo?— Can you open the file?
— A ver… sí, ya está.— Let’s see… yes, there it is.
Watch out
a ver
Do not confuse it with haber, which sounds identical but is a verb and never replaces this phrase.
Check yourself
Which one means “let’s see if it works”?