Thong Sala

Thong Sala is the main port and largest settlement on Ko Pha Ngan.

Get in There are ferries from Ko Samui to Thong Sala every day, the journey takes about an hour.
Departing Nathon multiple times a day for 200 baht.
Departing Mae Nam at 12 noon for 200 baht.
Departing Surat Thani multiple times a day for 250 Baht (3 hours + 1 hour bus ride from train station), or 400 Baht for the fast ferry (2 hours + 1 hour bus ride from train station)

At Thong Sala there are taxis and pick up trucks waiting to take passengers around the island, holding up signs with the destinations.
Price is a fixed 100-150 baht/person to Haad Rin,
150 Baht to the northwest corner of the island,
200-250 Baht to Thong Nai Pan.

Don't take taxi from pier after arrival but walk from there to the roundabout where you will find taxi station with better (not newcomer inflated, but still high as anywhere on island) prices.