Just like other Web3 applications, Zapper doesn't require you to register with email and passwords like a traditional software. Instead, you would connect your Ethereum wallet through one of the many options available including MetaMask, WalletConnect, Fortmatic and more (see screenshot below).
If you don't have one, a good place to start is MetaMask. You can visit their websites here. Remember, you can connect multiple wallets or paste in the address by clicking the dropdown menu next to your wallet address in the top left next to the Zapper logo and choosing Manage Addresses to paste in a valid ETH address or your ENS domain.