Nitric oxide is a miracle molecule which relaxes the arterial wall. The relaxation of the arterial wall means wider open blood vessels and that results in better blood flow.
Better blood flow causes increased delivery of the nutrients to the tissues all over the body. Nitric oxide also helps in decreasing the blood pressure naturally without taking the drugs.
This is the picture of relaxed arteries and the unrestricted flow of blood.
The picture of the constriction