Use the word vault in a sentence?

It depends on what way you're using the Word. It can be a verb or a noun.

As a verb, it means to jump over something, so an example would be:

"In order to complete the obstacle course, he had to vault the fence."

As a noun, it means a locked place where something is kept, like a bank vault, so a sentence would be:

"The gold bars were contained in a locked vault that was difficult to open."