I'm 18 and impotent, and I don't know what to do
Why do you think you are impotent?
I consider myself impotent because I can't get any of the girls that I like
Impotence is a medical condition that can be treated, but it has nothing to do with success in romance.  You need to find a girl who is interested in you, and shouldn't think of them as prizes to be claimed.
You don't give good advice, so I'm going to get off the computer now, I was joking anyway.
If you feel offended it says more about you than it does me. You can just ask or talk to girls you might be surprised how it goes. Girls like confidence.