Im new to this so what is CK and modding?

CK is the Creation Kit, the tool with which the game content is made. Modding is short for modifying, it means you change the game. Bethesda often releases a public, slightly limited version of these tools for their games so the players can change the game to their liking and most players release their 'mods' on the internet so others can use them.

ok, thanks (: oh and what does NPC mean?

Non Player Character