In order for ChannelMix to have access to your Salesforce Marketing Cloud account, previously ExactTarget, you'll need to connect in the Connect Page of ChannelMix Control Center.
We will need access to an API user. To set up an API user, please follow the directions here.
When connecting, be prepared to provide a Username and Password for this connection. The Connection Name is something you create, like "CLIENT NAME_YEAR_USERNAME".