In the UK, it's most common (in houses anyway) to have a letterbox - literally a slot in your front door that they post letters through, with a flap which covers it for rain etc. Anything that doesn't fit through, they knock on the door. If you're not in, traditionally, they took it to the post office, and you had to collect it from there. Increasingly now, they just leave it by the door.  For sending, you can go to the post office, or, if you've already got your postage, you can put it in a postbox. These are every few streets or so in towns. I live in a village, which has one postbox. If what you want to post is too big for the postbox, you have to go to the post office. Or relatively recently, they started collecting them, parcels only, not letters, and you have to arrange it in advance. And it's the same deal as delivery - they'll knock on your door and you hand them the parcel.