Connect your Marketing Cloud user with your Salesforce user

Connect your Users in Marketing Cloud

• Login to your Marketing Cloud Account with your User.
• Hover over your username in the upper right-hand corner of the screen and click "Setup".
• Under Administration, expand "Users".
• Click Users > click your username > Salesforce.com Status > click “Integrate” > Enter in your Salesforce.com Username > Save Settings.

Note: If you don't have access to perform these actions, please work with your Marketing Cloud Administrator to complete them. 

Connect Your Users in Sales or Service Cloud

• In a separate window, log in to your Sales or Service Cloud instance with your user. 
• Navigate to the Marketing Cloud Tab within Salesforce.
• Click “Connect to Marketing Cloud”.
• If you are logged into your Marketing Cloud user in the same browser, clicking this button will automatically link the accounts.
• If you are not still logged in, you will be prompted to enter your Marketing Cloud user credentials and this will complete the user integration.

Considerations:

If you receive an error saying "There was an error communicating with Salesforce, verify your connected app is set up properly and try again" after attempting to enter your Salesforce.com Username in Marketing Cloud, then your Salesforce user is likely not configured for authentication with Marketing Cloud Connect. Please ensure that the "Marketing Cloud for AppExchange User" checkbox and "Marketing Cloud for AppExchange Admin" (if you are an Admin) checkbox are selected on your Salesforce user profile. The "Marketing Cloud Connected App" permission set will also need to be assigned to your user as well. Please refer to the "Marketing Cloud Connect User Types and Permissions" documentation and the "Set Up Authentication" documentation below for more information.

Additional Salesforce Help Resources:
Marketing Cloud Connect User Types and Permissions
Set Up Authentication
Marketing Cloud Connect Connected App
Connect Marketing Cloud API User in Marketing Cloud Connect
Manage Users