Remember that this is what parents are for. If you have a dad, show him. He'll tell you if it looks like something to worry about and your mom can look if you don't have a dad. Getting their input is a good idea. There is something called varicocele. https://www.healthline.com/health/varicocele It's common, about 20 percent of adolescent males have it happen. It's like a varicose vein. They form often during puberty. Typically it is harmless. If it causes pain or causes complications, they consider methods of treatment for it but often they just leave it alone. They do recommend that if you develop a varicocele in your youth that you see a doctor. I have absolutely NO idea if this is what is going on with you but as it could be, you should show your dad and see a doctor. Let me know how it goes.
To be more specific, the vein is red and is all twisty. It's very visible and looks swollen. It is located directly under the head of my penis. It is noticeable when im not erect. Fortunately it does not cause me any pain.