Most of the train stations in European continent do not have ticket gates. Sometime you have to validate your ticket before entering the paid area but physically you can enter the paid area without ticket. Then, many cities do not even have turnstiles for their metro(subways).
On the other hand, stations in Japan except in rural areas are equipped with ticket gates. Then all metros have the turnstiles at the ticket gates. Which means no one can enter the paid area without risking himself/herself(either get caught by the station staff or you will get hurt). Then, not like subway in NYC, you need a ticket to get out from the paid area.
There are four types of paid area in Japan:
1) The staff stamps/checks/punches the ticket of the passenger who tries to pass the ticket gate and collects/checks the ticket of the passenger who tries to get out from the paid area.
2) Turnstile(automatic ticket gate) stamps/checks/punches the ticket for entering and exiting the paid area.
3) There is no ticket gate but there is a IC card validating/reading machine. You have to touch the machine by your IC card when entering/exiting the paid area(platform). In case you do not have IC card but paper ticket, no need to validate it. Just keep the ticket till your final destination.
4) NO staff, NO machine/turnstile. Many stations do not even have ticket vending machine. In this case, mostly you have to pay inside the train, usually when you get off at the destination. If the staff does not collect the ticket or the fare inside the train and your destination station has no ticket gate, sometimes you have to put the amount into a designated box located at the station.
Then, there are two types of turnstiles.
1) You can put the paper ticket into the machine or you can touch the machine by your IC card. If you are entering the paid area, you have to take the paper ticket. If you do not have enough credit, you can not enter the paid area by your IC card. When you are exiting the paid area, paper ticket will not come out. If you do not have sufficient credit, you have to go to the designated machine to charge your IC card and then try again.
2) You can just touch the machine by your IC card. The procedure are same as 1).
Mostly in metropolitan area of Tokyo is now deploying more IC card only machine. Therefore I do not recommend to buy paper ticket each time. Then, it is quite difficult for foreign tourists to buy the paper ticket due to the fare is not same for all stations(destinations) and Japan does not have ZONE system. Therefore you have to check the station on the map or the table and check the fare each time.
By the way, for Japan Rail Pass holders, you have to pass the ticket gate with staff located each time. If your station does not have any staff, you do not have to shown your pass to anyone.
Then, please note that station which Shinkansen is running mostly has three distinguished turnstiles.
1) To enter/leave from the paid area of Shinkansen
2) To enter/leave from the paid area of local trains(JR lines) - including limited express
3) To enter/leave from paid area of Shinkansen but leaving from/entering to paid area of local trains
Stations which only Shinkansen has only 1). Stations without Shinkansen has only 2).
Especially if you are transfering from Shinkansen to limited express or local train, please use turnstile 3).