What does "blow someone's mind" mean?
When do you use this phrase?

Bir çeviriye bakın

To "blow someone's mind" means to really impress them!
For example:
"The orchestra's music was amazing, it blew my mind!"
"How fast she could run was mind blowing!"
"Have you seen the new Batman movie? It will blow your mind!"

It can also be said when you hear or say something that makes you think of something you never have before.
For example:
"There are as many atoms in a grain of sand as there are stars in the universe, isn't that mind blowing?"

I hope that helps. :)