Porto is considered the second most important city of Portugal, located in the north of the country, about 3h driving time from Lisbon, the capital.
The easiest and most comfortable way to reach the city center of Porto, is definitely by car.
Please see my article here: https://lisbonguide.org/car-transfer-from-lisbon-to-porto/
But, some guests might prefer to check alternative options for transportation by public train.
There are several trains departing from Lisbon to Porto. Most of the trains will have 7-10 stops, and you will need to chabfe trains once at Campanhã, to reach Porto center (Sao Bento).
It takes around 3h30 to 4h, including stops on each station. There are also some direct, nonstop trains to Porto, named ALFA.
All trains are operated by CP.
You can find more information on their website: https://www.cp.pt/
For example, searching for a random day next month, I see 19 trains leaving to Porto from Lisbon. The first one departs 6h39AM from Lisbon Oriente, towards Porto (Campanhã), stopping 10 times. Then, change train at Campanhã, and take the other train to the center (Sao Bento).
Once arrived at Porto Sao Bento, you might need to get another transportation method to your hotel, depending where is located.
Hope this information can help, any questions just ask.