Hi, what would be the easiest way to get from shenzhen (luohu) to hong kong island?

You may cross the Luohu border, and take MTR East Rail Line to Hung Hom Station. Next, transfer to West Rail Line to East Tsim Sha Tsui Station. Then, transfer to Tsuen Wan line to Admiralty Station. After that, you may take Island Line or bus lines to your destination. You can buy tickets on the spot. Don't worry. :)