I'm 18 years old, I'm having pimples problem from the past 3 years and they leaving stains on my face, which resuls?

Acne vulgaris. This is hormone related and the stains may be scars. Not sure what you mean by the stains. The acne can extrude sebum. If you pick at them you may lead to scarring.
Treatment. I guess you want to know about treatment options, although, your question doesn't sound like that. There is a host of oral and topical meds that can be used. The most common approach is oral antibiotics - tetracyclines (doxy or minocycline). Make sure you have a good birth control option. Topical options are also available, although, you might have to go through a few options.