In order to enable generation of invoices (factura electrónica) via LibreDTE, navigate to Property Settings / Integrations and select LibreDTE section.
The details which you need to enter there must be obtained from Libre DTE account (https://libredte.cl/usuarios/perfil).
When the connection with LibreDTE is active, you can generate an invoice (Boleta or Factura de exportación) while taking payment.