To kick it all off, you'll first need to decide on a couple of things; which coin-pair you wish to invest in, what multiplier you wish to play at, and, whether you want to go short or long on the coin-pair.
If this is your initial transaction into the coin-pair, you are allowed to send as much P4D as you wish and it will represent your multiplied stake for each investment after that. For example, as the base cost is 100 P4D, if you sent 1,000 P4D it would mean you would get 10x the shares you would of if you just sent the base cost. Please note that the minimum amount that you can send is the base cost so all multipliers under 1x will revert and send back your P4D.
After this point, your multiplier is set for all additional transactions and you will be required to send the same amount of P4D you sent when you started. The only way you can alter the multiplier is by withdrawing and starting over again.
Short vs Long
Cryptocurrencies tend to go up or down in value so it's important to be able to choose a direction you think it'll go. If you think a coin-pair such as ETH-USD is going to increase in value over time, you would be taking a long position on the pair. In this example if you think that the USD is going to do better than ETH you would be taking a short position on the pair.
You can set the direction upon every new investment so if you can ride the peaks and troughs with each invest, you will most likely be averaging much higher than other players and therefore your proportional stake will be worth more than you have invested up to that point (ie a net positive position).