Most directories contain two special links, . (dot) and .. (dot dot).
So, for example, you could list the contents of the directory above your current working directory by typing:
ls ..
If your current directory is /home/fred/my_apps/favs, you could list the contents of the root directory by typing:
ls ../../../..
but the absolute path (/) is much shorter, and you don't have to figure out how many dot dots you need.