Up refers to the directions that are above. Down refers to the directions that are below. People use up and down when they refer to the direction that is straight ahead also. For example, "the bathroom is down the hall" means that it is straight down the hall. One can say that "the shop is down/up the street" and mean the same thing. Also, up usually refers to North and down refers to South, but most people don't take heed of that when they say "it's down/up the road". Two people who live in the same house could say "I live up Morse Street" or "I live down Morse Street". There are a lot of ways they can be interchanged. But of course, saying "up the stairs" is different from "down the stairs". Sometimes, they don't even refer to any direction at all. For example, "I live a few doors down from you". This doesn't mean they live below you or straight ahead, but somewhere to the left or right. The more you use them, the more you get the intuition for them.