Using Blockchain Wallet browser version only, open Setting > Addresses. Then click Import Existing Bitcoin Address. You can enter WIF (Wallet Import/Export Format) or compressed private key. Also you can scan QR code keys from paper wallet. This will allow you to actually send and receive bitcoins to and from this bitcoin address.
Site may propose you to transfer all bitcoins from imported address to integrated HD wallet. This is for your security. But you can keep imported keys with new address into wallet, without transfer.
Bitcoin and Bitcoin Cash private keys is same. After private keys import, you can check balance on both cryptocurrencies just swithing networks.
Read more at: https://allprivatekeys.com/how-to-import-private-keys.php