What are the Best Ed medicine available online Please suggest low cost and legal medines??

i talked with doctor last night "Here is what he says about ED drugs"

A man is sexually enthused when a gas called nitric oxide (NO) is released and helps relax the strengths in the penis. As the muscles relax, the penis is able to fill with blood and become erect.
Oral ED drugs help increase the effects of NO to assist men who have trouble getting or keeping an erection.

What Ed drugs does helps you get and keep an erection in response to sexual stimulation