What rail station in Barcelona for trains to Girona

You’ll need to go to the Barcelona Sants station for trains heading to Girona.

You may check train schedules here: https://www.renfe.com/es/en

Girona is a beautiful city, enjoy!

It depends on which train you're taking.

For fast trains (AVE and AVANTIA) you indeed need to go to Sants Estació (best option). The journey takes 40'. The website for fast trains is www.renfe.es as mentioned above.

But if you are not in a hurry you can catch a slower and cheaper train (Regional 'R' and Media Distància 'MD') that you can board in Passeig de Gràcia station, in a more central location. The journey takes between 1h15' and 1h30', depending on the type of train. Note there are hourly trains for this type of trains. Check details in www.rodalies.tk

The people on the R trains will be more interesting. :-)
Facing the counters on the ground level in Sants, get a ticket either from a machine or from the left side of the human ticket lines, and take the escalator down to the tracks, also on the left.
There may be touts by the stairs offering to drive and/or provide a tour as an alternative to taking the train, but I think they are really trying to fill up a bus or van even though it looks like they're a personal guide.