I'm trying to understand.
So my btc I already own allows me to get bcc from it. What happens to the old btc?
You get to keep both.
If you have 1 BTC before the fork, after the fork you'll have 1 BTC + 1 BCC. If you have it on your wallet or an exchange like Kraken who promised their users their respective BCCs. If you're on Coinbase you won't get your BCC, i recommend you withdrawl your BTC as soon as possible to your wallet or a different exchange for august 1st.