"Noord" means northern and is only used in geographical names. It is either used as prefix (usually with a hyphen), or after a geographical name:
- Noord-Amerika - North America
- Noord-Holland - name of the province that Amsterdam is in.
- Amsterdam Noord - the northern part of Amsterdam.
There is also the adjective "noordelijk", with means northern in all other contexts. "Noordelijke wind" - northern wind.
"Het noorden" is a noun, you will encounter it much more often than the above words. Aside from the cardinal direction (the north ), it is also used as a direction of motion:
- Ik ga naar het noorden - I go North.
- Hij woont in het noorden - He lives up North (or: in the North)