The VAT number (Umsatzsteuernummer, Umsatzsteuer-Identifikationsnummer or USt-IdNr.) is for businesses that charge VAT. In Germany, the VAT number has this format: DE123456789.
You can request a VAT number when you register your business with the Finanzamt. You can also request a VAT number here.
The VAT number is not the same as the tax number (Steuernummer).