Apps purchases pop-up options
To buy something on the App Store you have to type your password. 

If you choose "always require", every time you buy something, App Store will ask your password. 

If you choose "Require after 15 minutes", for the first purchase you will have to type your password, then you would be able to buy everything on the App Store for 15 minutes without typing your password again. 
After 15 minutes, App Store will ask your password again.