You can plant different vegetables, that can be sold after they get ripe. The sell value depends on the vegetable quality. And vegetable quality depends on the other plants, that grow close up to it. All the influences are written in helpfull popups. If vegetable quality is toooo loow, than you would get no money for it. So keep your plants fresh and cool! Also, you can buy bonus items, that will be encreasing your vegetables qulity on each grow stage.