The side which is the left of the stick when the hook is facing away from the body. For almost all sticks, this will be the flat (or flatter) side - there is normally a noticeable difference.
You use the flat side of the stick. In a game, if you use the curved side a foul will be awarded against you.
The hockey stick was invented to use along with the hockey puck in the game of hockey. The Mi'kmaq people of Nova Scotia are credited with inventing the hockey stick.
a hockey stick a puck
No, you can only use the flat side of the stick. You can never use the round side.