You are the garden gnome driving the power mower. Watch out for birds flying by, specially the bird droppings, you should hit them with tomatoes. Also keep an eye on the ground, you have to jump over the obstacles - or actually shoot them with tomatos. Use the UP key to jump, the LEFT and RIGHT key to drive faster or slower and press SPACE to fire tomatoes.
If you are able to catch the umbrella, you are safe from the bird droppings. Try also to collect the fruits passing by, you get extra points for them!