You can claim bitcoin forks only if you have Bitcoin in your wallet before a particular date or block height on bitcoin blockchain.
Second thing to know : Who will create this fork will give you a website or a wallet for claim this fork. You can find this website on airdropalert.com.
You can claim your fork only when you will reach the date or block height when the fork will happen.
Sometimes can happen that your Bitcoin wallet doesn't support the new fork.
So...What to do in this case?
1)Export your private key from your bitcoin wallet.
Important Note: every Bitcoin address on your wallet has its own private key. If you have a wallet with bitcoin address that is TTYKJKBJGH1111, you have to look for that address in your wallet and to your right you will find your private key. Copy it.
2)Download a new wallet that support Bitcoin and the Bitcoin fork.
3)Import in this new wallet the private key that you take from your Bitcoin wallet
4)Now you have in this new wallet a balance of Bitcoin.
5)Create a new address in the new wallet for the new fork adding the name of fork.
6)Now the wallet will recognize that you have bitcoin before forks and it will give you an amount of crypto fork.