Puberty is a journey, not a single location in time. Your ability to produce semen (including sperm) will come within the next year assuming your testes are in their correct place in your scrotum.
During early development in the womb, the testes (balls) are both inside the baby's abdomen. They normally descend into the scrotum (ball sack) some time before birth. One of the checks that is made immediately after delivery of a baby boy is that his testes are both in the scrotum. If they are not both descended then further checks are made until he is old enough to safely have an operation (called orchidoplexy) to move them into the scrotum and anchor them there. Note that it is particulalry rare for both testes to be undescended at birth.
Initially, the scrotum is quite small, as are the testes which sit very close to the body. During puberty the scrotum lengthens (as does the penis) and the testes drop down into it so that they lie at the bottom with significant space above them. (This is what is meant when we say "the balls have dropped".)
Every child should have a thorough medical checkup around the start of puberty (often done during the last term in the primary school) and again the doctor should check that the testes are both properly in the scrotum for a boy.
If a testicle remains in the body, rather than being in the scrotum, then it cannot do its job of producing testosterone and sperm. It will tend to atrophy and can become cancerous, which is why proper checks need to be made during childhood and before puberty. If indeed both of your testes are not permanently descended into the scrotum you MUST inform your parents and ask to see the doctor urgently so that the problem can be resolved quickly.