Once in the game you can you WASD to move, and (SPACE) to throw a spike. that is what's used to collect Tomatoes. you'll have to send your Tomatoes to Tom, (Phone to the left) once you have collected 15. the shop can be accessed to the right, at the Little Tomato stand. Tomatoes drop at a rate of 10 every 10 seconds, unless you have the faster Tomato upgrade which will bring it down to 8 seconds.
WARNING: The game Auto-Saves every 2 minutes, Please make sure you go to Title Screen via the Menu button to save current progress before you leave.