Does USPS deliver to your mailbox or door? 10 POINTS!!!!!!?

Hi I was just wondering where my pacakge was because it says it has been delivered on the website. My package is realy really small because i ordered contacts. Usually when i order things online they show up at my doorstep but does USPS do it deiffrently and put it in your mailbox?! and if it is in my mailbox how the heck do they get inside there?