If you had BTC in Coinbase during the split, Coinbase automatically handled the split for you and provided the appropriate amount of BCC in a separate account.
If your BTC lives in a wallet outside of an exchange that automatically handles the split, you need to use a BCC wallet (like Electron Cash, for example) to read the BTC wallet information, notably the private key. If you have the private key for a specific BTC wallet, that key also works for the BCC wallet.
If you are paranoid, move the BTC to another wallet before trying to access the BCC represented by that wallet, since the same key can be used to empty either the BTC or BCC wallets.
Personally, I used Electrum for my BTC. I swept my old BTC into an Electrum wallet and them moved it to a Coinbase BTC account. After that, I used Electron Cash on the same wallet to move the BCC represented in that wallet to Coinbase BCC account. Don't get confused. BTC sent to a BCC wallet or BCC sent to a BTC wallet are lost, forever.