When you open word, a selection of different types of new documents will appear. This will open a list of letterhead templates. You can also download customizable templates from the official site of Microsoft Word. Go to the site, type "letterhead templates" in the search box, and download the template you want. Open your template in Microsoft Word and start customization. Update your company's title, contact information and logo. Press the Esc key to close the Header and Footer sections. View your letterhead stationary in full screen mode or print a copy for review. When creating a new document on this letterhead, open the letterhead file and click "Save as" under the Office Windows logo button.

TL;DR in Indonesian:
Buka Word. Pilih kategori kepala surat. Ubah kepala surat Anda. Cek ulang kepala surat Anda. Simpan kop surat dalam hard drive Anda.