You need a fiscal representative if you are legally registered in Country A, but you have some operations in Country B that requires you to be registered for tax purposes in Country B. As you are not legally registered (with a local address) in Country B, you need a representative/agent to represent you towards the tax authorities if they need to contact your business. Furthermore, in some countries this information must be on the invoice.
If you add a fiscal representative, this is associated with a tax registration number that you set up when adding a legal entity. See Setting up E-Invoicing for more info.
Add fiscal representatives before setting up a legal entity. This ensures that you can assign your fiscal representative to your legal entity.
On the left of the Admin page, click on the Fiscal Representatives link and on the Add Fiscal Representative button.
In the appearing window, fill in at least the mandatory (address) fields (marked with a red asterisk).
The entry appears in the table on the Admin Fiscal Representatives page. Click on the Manage button in the right corner of the table to manage/edit the information for your fiscal representative.