How do I open Airdrop on the Ipad mini?

How do I open Airdrop on the Ipad mini? I can see that if I select a photo(s), and then select "Share" Airdrop comes up as a way of sharing.....But then what? If I select it nothing happens.

Also, If someone wants to share pictures with me....How do I turn it on (Airdrop), so that the Ipad mini shows up on their screen?

Many thanks for any help.

Kathy