Tan Lotion help!??!?!?!?!?!?

so i was thinking about buying Neutrogena Build a Tan Gradual Sunless Tanning Lotion, but i really dont know how it works.. do i just keep putting it on my body? or do i have to put it on like once a day or something.. will i get the tan i want overnight or will i have to wait a couple of days?