The Teamgo "Customer" user type is associated with the supplier module. When you have the Supplier module enabled on your Teamgo service plan it will enable two new user types under the User menu option.
These are business's that supply services to you. When you setup a company you can load their contractor workers or let them load their own contractors. This is useful for tracking people external to your organisation but may supply services to you and need to be tracked accordingly.
Likewise with "Companies" the "Customer" user type are the organisations you supply services. So if an organisation invites you to be a supplier for them, you will see these organisations listed under the Customer option and they will see you under their Companies tab.
There is not a lot you can do with the Customer tab other than view who you have become a supplier to, but you can Export your customers to a CSV file.