Flying from USA to Hong Kong and then a flight to Guangzhou.

Here are the transfer procedures if you do not hold an onward boarding pass.
Step 1: Check your transfer desk's location
Step 2: Go to the designated Transfer Desk Areas E1, E2 or W1 for check-in
Step 3: Go to departures level for boarding gates
Step 4: Go through security screening
Step 5: Check your gate number and time, and reach your boarding gate at least 30 minutes before departures time.

If you hold an onward boarding pass, the first two steps can be omitted.

Yes! You can go to see Big Buddha or Disneyland Resort during the layover. Have fun! ;)