If a fork is introduced like what happened with bitcoin cash, you'd get the exact same amount you have as bitcoins in the new fork.
So for example if you have 2 btc, you'll 2 Bitcoin cash.
As simple as that. You just need to have your money in a wallet or an exchange that supports the new network.
Personally I had not that much coins and I put them on Bittrex (actually kinda dangerous) but ended up getting the same amount on 1:1 basis.
You should read this. It's useful.
https://bitcointalk.org/index.php?topic=2012799.0