Dear [Applicant Name],

Congratulations on your recent visa approval!
 
Please note the visa/entry permit label should be affixed onto a blank visa page of your travel document for presentation to an immigration officer upon arrival in the Hong Kong Special Administrative Region within three months from the date of issuance. 

For the Visa Activation:
If the Applicant is IN HONG KONG:
First, please exit Hong Kong's border via airport or land boundaries (Macau, Shenzhen, Zhuhai...etc).  When you are outside Hong Kong, please stick the visa label inside your passport. 
If the Applicant is NOT IN HONG KONG:
Please come to Hong Kong.  Before you go through the immigration, please stick the visa label inside your passport.
Then:
Please present the visa label for an immigration officer's examination at Hong Kong's border when you enter/re-enter Hong Kong.  He/she will stamp the visa label with "journey completed" and state the expiry date of your new visa in your passport.  You can use the Hong Kong resident counter to do this.
Once the above activation procedure is completed, you need to arrange for the Hong Kong Identity Card procedure.
It has been a pleasure assisting you and we wish you all the best in Hong Kong!