To download the database of partners (counterparties), you need to go to the "Contacts" module. Click on the "Bookmarks" - "Import records" button:
In the resulting window, you can download a ready-made Excel file template for importing partners into Odoo:
You can also use your Excel file.
In this case, you will need to make a little more settings to import data correctly.
Next, click the "Upload file" button and select the file from which the data should be uploaded:
A window will open in which the fields in the Excel file and Odoo are mapped.
If you used a ready-made template, these fields will be filled in automatically, if not, you will need to configure them manually: 
After making all the settings, click the "Test" button:
If there are no errors, then click "Import":
After that, we check the downloaded data.