Drag the cursor to aim, click to fire. To start, click on the "next round" button to advance to the next round. The lower the reload speed is, the faster reload that you have. When you decide to get upgrades, click on the green arrow to go to the upgrade menu and click on the upgrades to buy them. To leave the upgrade menu, press on the red X that replaces the green arrow. You can't shoot in the red space at the beginning of the track.
A big thanks to Odieagle2, and CrazyBerserk. DO NOT CLICK THE NEXT ROUND BUTTON REPEATEDLY!!