When doing imports, the most efficient way is to use the Dynamics 365 form import templates, these make the process a lot easier if you are not familiar with importing data using different methods. Please see the below steps in order to retrieve these templates.
Navigate to the settings tab in the Dynamics 365 site map
Then navigate to the Data Management section
We will then open the templates for data import section and this will pop open a new tab,
You will then need to choose your template based on which entity you are looking to import.