in medical term it is know as Peyronie's disease
Many men have a slight curve in the penis. As long as there is no pain or problem with sexual performance, men with a slightly curved penis should not be concerned. They do not need to see a doctor.
CAUSES : 1)by birth
2)scar tissue formation due to trauma or accidental injuries
WHEN TO WORRY/SEEK DOCTOR :
1)difficulty while doing sex
2)pain while doing sex
3)erection problem
4)significant observable curve developed
Treatment:
Most men with curvature of the penis do not need any treatment. This is true regardless of the cause.

Men with Peyronie's disease who experience pain or difficulty with intercourse may be offered treatment with verapamil or collagenase penile injections. Potential oral drugs that may help include pentoxifylline and coenzyme Q10.

Corrective surgery may be offered to men with more bothersome or disfiguring symptoms that persist for more than one year. It's important to make sure that the disease is not active at the time of surgery. So, surgery should be delayed for at least three months after the condition is clearly stable.

In a typical procedure, the inflamed or scarred portion of tissue is removed from the penis. It is replaced with a graft taken from another part of the body (often the scrotum or forearm).

This surgery often works well. However, mild curvature of the penis may remain. In addition, sexual function or shortening of the penis may not improve following surgery.
PROGNOSIS:
Some men with Peyronie's disease improve without treatment. Other men have mild symptoms that can be tolerated. Because they do not interfere with sexual activity, these men may choose not to seek treatment.

Only a minority of men eventually will require surgery.

Peyronie's disease does not develop into cancer or other serious conditions.
I hope u satisfy with my explanation.