how do i get hong kong invition letter.I am from Ghana and need to visit HK for holidays

If you join a tour to visit HK, you can ask your tour agency to issue you one.
If you want to visit your friends or relatives in HK, you can ask them to write you one.

If you travel alone, the invitation letter is not necessary. You can use your flight tickets and hotel bookings, proof of visiting purposes and bank statement for application.