Buy salt and strawberries for your ice cream slug and profit big from the ice cream he makes. Invest in the items you think will go up in price, but make sure to buy beer for all of your slugs or else they die. Just cross your fingers that none of your slugs become turd slugs or zombie slugs.
All actions are performed with mouse clicks. See the in-game tutorial. It will show you how to play, as well as some basic strategy to succeed in the game.