You can’t login to cTrader with MT4’s login credentials.
cTrader and MT4 are different platforms, thus you need to open two different accounts to log in to each of them.
To open a real/live trading account for cTrader, you need to visit a broker’s website(which offers cTrader as a trading platform) and go through the account opening process.
Each broker offers different trading platforms and account types.
You may visit the page below to compare these brokers in the table.