How do you prove something exist when you can't see it?

"How do you prove something exist when you can't see it?"

"Does the GOD exists? Does the wind blow?"

Someone answered " We know because the leaves move."

" So then, we'll look for the effects! It's simple isn't it?"

Some nice place on the Earth that I wish I can be there someday...They're amazing!

Niagara waterfall

Yosemite Valley