It may be Prominence of a Vein or veins in the Scrotum
.If they are visible in standing position and disappears when you lie down,it may be Varicocele
If the swelling appears in the groin region or just above testis after any pressure,it may be Inguinal hernia
Any disease will be confirmed by General surgeon/Urologist
.Nothing to worry.
If the Testis is of normal size,Cancer is excluded.