Which train station should I go?

I have taken that train several times. Santos. You can take a subway from different parts of Barcelona to get over there. It was slightly confusing because you come out of the subway and then you have to walk a block over to the train station. Leave yourself plenty of time because they have a full x-ray machine security System before you get on the high-speed train. When confusing about Barcelona is that they have two different subway companies in their tickets are not interchangeable.

You don't get to choose which station, as they don't all have trains to everywhere. There will be a choice for, say, Barcelona (all) and once you choose start and destination cities it will default to the stations that serve that route.

Does the hotel's website say which train station they are closest too? If not, can you contact your hotel and ask the best way to reach their hotel via public transportation? I've taken both the train and bus and prefer the bus over the train. Of course, this depends on what neighborhood you are staying in.

The express trains between Barcelona and Madrid use Barcelona Sants and Madrid Puerta de Atocha. Those trains wouldn't be so fast if they made many stops, so you don't have a choice on which stations to use. Any time you see "(Todas)" after the name of a city on the Renfe website, it's a way for you simply to choose your origin/destination city and let the website tell you which station the train will use. You can see that information on the results page by clicking on one of the listed trains and then on "See details of the route".

If you look on Google maps you will see that the closest metro station is Camp de l'arpa on Line 5.

From the city transport website take that 7 stops in the direction of Cornella Centre to reach Sants Station for the train to Madrid- https://www.tmb.cat/en/barcelona/metro/-/lineametro/L5

This is one of the available maps of the Barcelona metro (the one which I use overlaid on to mapping systems) but I am sure there are others which will better suit folk here.- https://urbanrail.net/eu/es/bcn/barcelona.htm

This is the map from TMB which also shows the RENFE (main line) stations listed- https://www.tmb.cat/documents/20182/96078/Pl%C3%A0nol+xarxa+de+Metro.pdf/f5578f40-5a66-46ba-907c-cf31e0d368c0?t=1706099890696

When booking if you don't use Barcelona Todas as your origin and Madid Todas as your destination you are liable to get odd results.

The TMB journey planner will show you routes by bus involving routes H8 and H10- you either have a walk at one end of the journey or another or have to switch between the lines for an almost door to door service.