Bangkok to koh samui? By train?

If you take a train your have to go to Surat Thani and then a bus or mini van to the ferry about 40 minutes away. Then take the ferry another hour and half to Samui. You can also take a bus from Bangkok to the pier in Surat Thani and then the ferry. You can get an overnight bus and arrive in the morning at the pier. If you fly only Bangkok Airways and Thai Airlines fly directly to Koh Samui google them to find there web site and price. I think it's about $240 or so round trip but prices are going up plus baggage allowance is only about 10 to 20 kg and you pay a lot extra for luggage over that limit. I think I have told you this about 3 or 4 different times you have asked this same question. You need to decide what you want to do and do it.