You will find two ferry terminals on the mainland at Laem Ngop, everyone will end up at either one or the other and both take vehicles and passengers.
Ao Thammachat pier is used by Ferry Koh Chang, the ferry sails between the hours of 06.30 – 19.00 and runs every 45 minutes. You will arrive at Ao Sapporot pier on Koh Chang, and the charge is 80 Baht for passengers and 120 Baht for cars one way. This is the better of the two ferry piers.
The second pier is Centerpoint pier and is used by the Centerpoint Ferry company which allows cars on free of charge and passengers pay 80 Baht. The ferry runs each hour between 06.30 – 19.00 and arrives at Dan Kao pier on Koh Chang.
There aren’t any passenger only boats or speedboat services from the mainland to Koh Chang.
Link to ferry timetables and information: