It could be one of many harmless things. Many guys have some kind of junk on their junk. Like Dave said, tell your parents so they can set up a doctors visit. We know this isn't an easy thing to talk to parents about. You can tell them you found something suspicious while doing a self-exam like you heard about in Health class. If you were my kid (mine are older than you), I would make the appointment right away. You are probably due for a physical anyway, and probably ready to graduate from a pediatrician to a regular family physician.
Hope this helps. Let us know how it goes.
"Statistics are human beings with the tears wiped off" - Paul Brodeur
Diagnosis: 05Sept07 Right I/O: 13Sept07; Pure Seminoma; Surveillance only per NCCN: All Clear February2013 (Chest Xray, Markers); Next check August2013 (CT Scans, Markers)