Your cTrader credentials are sent to you via email once the creation of your account has been confirmed.
Once you open the platform, you will be presented with a login box, or you can go to 'cTrader'
in the top left hand corner, and select 'sign in'
Enter the account number and copy and paste the pasword you have received via email.
You also have the option to 'Sign In with your cTrader ID'
, and if you do this you can link all of your cTrader demo and live accounts to it, so that you can simply log in with your cTID and easily switch between trading accounts.