I assume that you have a business number (BN) and a WAC.  You can start in Profile menu EFILE Options, where you enter the Business number (transmitter number if you like). The business number must have 15 digits. If you are filing T4 it will most likely end with RP0001.  

Then you will EFILE, this will create the XML and it will  take you to the Profile CRA portal. It will asks you to enter the account number and WAC. For the account number you must enter the same BN that the one you entered in Profile Options, and the WAC associated to your BN