Okay so I know headaches mean different things so if I have a headach behind my left eye what would that be? My eye feels bruised.

Depends. Lots of people have "retro-orbital" pain. It's common in migraines. So it could be nothing, or it could be a tumor or aneurysm growing behind your eye. The "bruised" feeling is most likely just your brain's interpretation of this particular pain. Also depends on whether it's new or not. But a definitive answer should come from your doctor, not this website.
Headache treatment. As you stated, headaches are non-specific. You could try otc headache medications and artificial tears to lubricate the eye. If the headache does not resolve, become more severe, develops other associated symptoms, or has associated blurred vision, you need to see an eye doctors as soon as possible.
Headache therapy. You can try some otc headache medication and artificial tears to lubricate the eye but if the headache worsens, does not resolve, develops other associated symptoms including blurred vision, then you need to go see an eye doctor. Cool compresses around the affected eye can sometimes help as well.