Hi,
Did you have any scrotum injuiry in the recent times? Nevertheless, such cysts are quite common, and you need not have to worry much, but should always be checked by a doctor. Please consult a urologist for proper diagnosis.
Solace
It's likely a benign hydrocele, spermatocele, or varicocele. Lots of men get them and they typically don't cause complications, but it's best to confirm with a doctor anyway.