Let's begin with http://www.cnet.com/how-to/getting-started-with-user-accounts-on-android-5-0-lollipop/
I have a son, he likes playing my phone, but you know, on my phone, there are many secret photos, so everytime he plays my phone, I'm afraid that he may see them.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic