The template
Replace the bracketed fields as you go: [your business name] takes your registered name, with a tagline or registered activity on one line, and your contact line: P.O. Box, town, Namibia, phone, email, website. Nothing in brackets should survive into the printed letterhead.
Then the letter itself: date, recipient name and title, address, and "Dear [Recipient]". The body carries one idea per paragraph, plain language, no filler. It closes "Yours sincerely" over a signature, name and title.