It could just be an irritated nerve - have you twisted your body funny or maybe injured yourself?
Most likely, it's benign fasciculation, which is the clinical name for muscle twitching. Benign, medically, means "not harmful". It can happen anywhere on your body. If your eyelid has ever twitched, or your thumb - it's the same thing.
Do you feel any swelling, pain, tenderness, lumps? Anything out of the ordinary?
If you start to feel any pain at all - seriously, like any - tell your parents. I know it's embarrassing, but there are conditions that sometimes require immediate medical attention. I don't think you have any of these, but they're things to know about, just in case.
(Most of these links have pics that you probably want to view alone. They're illustrations, but still...)
The most serious is testicular torsion. I doubt this is what you have, because this would be some serious pain, but it's worth letting you know about. It's when the blood supply to a testicle gets cut off for some reason, usually injury - https://www.urologyhealth.org/urologic-conditions/testicular-torsion This is a serious medical emergency, and if you feel sudden, severe pain, tell your parents immediately, and go to the emergency room.
You could have a varicocele, which is an enlargement in the veins. https://www.mayoclinic.org/diseases-conditions/varicocele/symptoms-causes/syc-20378771
You're also now in the age range for testicular cancer. Again, I don't think that's what this is, but it's something you should know about. https://www.mayoclinic.org/diseases-conditions/testicular-cancer-care/symptoms-causes/syc-20352986
I don't want to scare you - I think it's probably harmless. I just want to make sure you're informed.