Even though you can utilize any Dynamics CRM user account that has the System Administrator role, to set up the integration between SalesScreen and your Dynamics CRM organization, it can be smart to create an "API user" for this purpose.
First order of business is to sign in to your Dynamics CRM Online organization with a System Administrator account. Then, follow the official Microsoft information on how to create a new user account for Dynamics CRM Online.
Tip: Name the user something along the lines of "API User" or "Integration User".
The next step is to make sure the newly created user has the necessary privileges to read records for all users across the organization. The easiest way to ensure this, is to give the user the System Administrator role. Simply follow these steps.