An NPC is a non-player character. Basically anyone who is isn't controlled by a player (Romeo in Varrock, Varrock guard).
Chat with our AI personalities
There is no NPC, place, or item in RuneScape called "Kela."
Playing mini-games around the warriors guild, try talking to NPC's.
Talk to the banker NPC in-game about your key, should give you the option.
In order to gain Constitution Xp you must inflict damage on an NPC or in PvP and you will get 10% of the damage as constitution Xp.
Realistically, you have 3 choices; 1) Buy it from the Scimitar shop in Al Kharid 2) Get it as a drop from an NPC that drops it 3) Buy it from the Grand Exchange