After registering with the Trade office to register a company, you will receive the Fragebogen zur steuerlichen Erfassung per post after some days. This is in English the Questionnaire for tax collection.
Here is a translation of this form for commercial, freelance, or agricultural activity. This form is for founding a one-person business(Einzelunternehmen) or with multiple persons(GbR)
After you submit the form to the Finanzamt, you will receive your new tax number. Also, you will receive your VAT ID if you applied for it in the form.IchBerlin_Fragebogen-zur-Steuerlichen-Erfassung-English-Translation