Want to visit Taragona from Barcelona. Please offer detailed directions there and back from Barcelona using train. Would a stop in Sieges be doable in the same trip?

There are frequent trains - very frequent between Barcelona and Tarragona tha ttake about an hour - some are regional trains you can just show up and buy a flat-fare ticket and go but on the faster trains - 10 minutes all told faster about - you need a seat reservation which comes with the ticket and on these trains full-fare may be much more than booking in advance - www.renfe.com - good luck with that extremely fickle site!

For lots of info on Spanish trains check www.seat61.com - great info on discounted tickets; www.ricksteves.com and www.budgeteuropetravel.com. Sitges is I believe a dead-end station by suburban train from Barcelona so would not be on the route to Tarragona if I read schedules right.

There are a number of trains in that direction ( not sure about Sitges...I made it a different trip.)
If you returning to Barcelona on Sunday, the trains are often packed with students going
back to the city....we had to stand all the way back.

P.S.

Important.
DO NOT take fast trains that get you there in 35 minutes...they stop a few kilometers
out of town.
I checked RENFE,
no stops in Sitges on the way to Tarragona.

For Sitges, take the Cercanía commuter train from Sants. For Tarragona, either a train or bus.

Yes, Cercania to Sitges...about40 minutes.

Good info from danon about fast trains stopping out of town a few minute s- no wonder the regional or lcal train is almost as quick - to the town center that is - but as said above regional trains without their seat reservation requqirement can always be mobbed and SRO. But they are so so easy - just turn up and cop a ticket. Don't forget to cancel the ticket yourself before boarding if that is the policy - ask when buying it.