HK Free Airport Express Shuttle Bus Service to my hotel

The free Airport Express Shuttle Bus Service is not from the Airport Terminal? So, do I have to take the train from the Airport Arrival Terminal to Koeloon or Hong Kong Station to catch the free shuttle bus service? Where do I find the shuttle bus when I arrive at HK or Kowloon station? Which station is better as I am studying at Imperial a Hotel at Tsim Shat Shui? Or can I take the MTR to Tsim Shat Tsui station?