Fertilizers are chemical or organic substances applied to soil to help plants grow by providing essential elements like nitrogen, phosphorus, and potassium. There are two main types of fertilizers - inorganic chemical fertilizers that are made synthetically and provide nutrients, and organic fertilizers obtained from animal or plant sources that enrich soil quality. Fertilizers come in different forms and have benefits like immediate effects on crops and increased yields, but overuse can be toxic and damage soils over time.