Instructions
The trading window shows in real-time - already when entering credits - the potential credit winnings if you execute this transaction. If you are right, each share pays 1 credit.
Once you are satisfied with the indicated values, submit the transaction by pressing the green "Execute" button.
Mechanics
When investing credits "in favour" of an answer ("Long") and such answer actually does occur in the end (during final settlement), one credit per share will be credited to your trading account, if another answer occurs, the originally invested credits will be lost.
Vice versa, if you invest credits "against" an answer ("Short"), you win the potential winnings if another answer occurs in the end. Accordingly you lose the invested credits, if the answer actually does occur.