We will be staying 1 night in Sintra from Lisbon. I believe train is the best way to travel? Do we reserve our tickets in Lisbon or advance offers discounts?

Also what's the best way to travel from Sintra to Porto? Do we really have to come back to Lisbon? Do we reserve in advance?

For definitive information on trains, https://www.seat61.com

For information about how to get from place to place, see rome2rio.com, but be sure to check the links to which it directs you, as the main web page is not sensitive to seasonal variation in schedules.

Trains: https://www.cp.pt/passageiros/en/train-times
Buses: https://www.rede-expressos.pt/default.aspx

Sintra is a short commuter train ride - no reason to purchase in advance at all- Sintra-Porto yes check www.seat61.com for all relevant info on booking ahead for discounts but normal full-fare is not that much - other rail sites www.ricksteves.com; www.budgeteuropetravel.com.

For quick reference schedules www.bahn.de/en - German Railways site for all European trains just put in Sintra to Porto and see the connections.

www.bahn.de/en shows all connections to Porto from Sintra require going back to Lisbon's Oriente train station - 45 minutes and then direct to Porto.

I would suggest Sintra as a baggage-free day trip from Lisbon - hassle relocating for one night and Sintra is a small town- I'd rather be in Lisbon at night.

Or leave bags in Lisbon Oriente station day before.

The train to Sintra departs from Rossio station, not Gare do Oriente. There is luggage storage at the Rossio Metro Station.

http://www.citylockers.pt

You can catch trains to Porto from Rossio but with 2 changes of trins according towww.bahn.de/en

Don't use international hobby sites for official schedules... every single day it might happen some kind of update. My opinion.

As we can see in most answers, there's a lot of different opinions...

The truth is... yes, you need to return to Lisbon. Secondly, it's pretty straightforward - you need to take the direct urban train connection from Sintra to the Oriente train station. That was correct!
And then take the national trains, either the Alfa or the Intercity. Don't worry, there are a lot of daily connections.

Forget Rossio, on this one.

Don't use international hobby sites for official schedules... every single day it might happen some kind of update. My opinion.>

Of course go to the source for definitive updated schedules but bahn.de/en is great to get a fix on trains quickly when planning.

Hi, i'm from LIsbon

From Lisbon to Sintra you don't need to reserve your ticket.
There are, normally, 4 trains per hour from Lisbon to Sintra, it´s very easy it's a 1/2 hour train ride. You can buy the ticket in the train station, Rossio train station (central station), 2,1 euro per person.

From Lisbon to Porto you need to buy your ticket in Santa Apolonia (close to the cruise terminal) train station or Oriente station or online. No need to reserve it since the train never gets full. The departure station could be in Santa Apolonia station or Oriente Station. It´s not possible to travel directly from Sintra to Porto.
You can travel from Sintra to Oriente station and then from oriente to Porto, different trains.
There are several ones everyday.
The train site is

www.cp.pt

From Lisbon to Sintra you don't need to reserve your ticket.>

reservations not even possible on that, right?

PQ: >>Don't use international hobby sites for official schedules... every single day it might happen some kind of update. My opinion.>

Of course go to the source for definitive updated schedules but bahn.de/en is great to get a fix on trains quickly when planning.<<

I'm pretty sure Lisbon_Eagle was dissing seat 61 . . . (It may be a 'hobby site' but is one one of the most useful sites out there)

JJ- <I'm pretty sure Lisbon_Eagle was dissing seat 61 . . . (It may be a 'hobby site' but is one one of the most useful sites out there)>

It's not a hobby site - seat61.com - may have begun as one but now is a growing commercial site with a staff of at least seven employees I read and rapidly has become the most useful site for planning train tavel - especially your own online ticketing - out there and getting better every day.