I wrote about how the game is played on the main page, but I can summarize here, too! 

The game is played with the mouse. Clicking uses your current tool, and the mouse wheel scrolls between the tools you have unlocked. The green bar at the bottom represents your progress to the next upgrade. It'll progress when you place tiles, or when your flora and fauna mature or eat. The main page for the game has a field guide that explains what each creature does and eats. Let me know if you have any other questions!