Wifi?

My wife has new Kindle fire hd
the email address is Hotmail. connection Wi-Fi.

I noticed checking her emails clicking the mail envelope logo you go straight to inbox listing her messages (two) how do you actually log out or isn't it necessary using Wi-Fi connection?.
Sorry if I've missed something
On my pc, as you know, you can logout and have to enter email address and password to get back in but can't see logout or exit on the Kindle.
Many thanks