The Euskotren station, where the trains between Hendaye and both Irun* and San Sebastian/Donastia depart from and arrive at, is in the forecourt of the main Gare de Hendaye, SNCF station.
When exiting the station turn to the right - in the image above it is the small building with the blue sign attached to it.
Lasarte-Oria is the terminating station of most of the Euskotren services from Hendaye.
So if you're heading to Irun or San Sebastian/Donastia and see a train heading to Lasarte-Oria, then that is the train you need to take.
When arriving by Euskotren train, walk ahead of you when leaving Euskotren station and the SNCF station is the building over to the right.
When heading to Hendaye by Euskotren train, you need to take a train heading to Hendaia.
*Between Hendaye/Hendaia and Irun, the Euskotren train service is much more frequent than the mainline train service.
If you will be connecting at Hendaye between a TGV and the Trenhotel train to/from Lisboa/Lisbon, then it's likely that you will need to transfer between voies/platforms/tracks.
But stairs provide the only access to/from the voie/tracks/platform that the Trenhotel train will use.
This is one of more than 300 station guides available on ShowMeTheJourney, which will make it easier to take the train journeys you want or need to make. As always, all images were captured on trips taken by ShowMeTheJourney.