You can get from Lisbon airport to Porto city in various ways:

• by plane, as there is an airport in the city of Porto,
• by bus,
• by rail,
• by car on the high-speed line connecting the capital with the city of Porto.

You can rent a car right at the airport, and it is not necessary to book it in advance, several rental companies work here at once. But in high season, cars with the most favorable price / quality ratio can be reserved, so it's better to book a means of transportation in advance.

If second or third methods of transportation are interesting, then it is most convenient to get by metro or taxi to Oriental station in the "Expo" area where there is a station and a bus station, buy a ticket and go to the north of Portugal. This, perhaps, the most profitable ways (the cost of a one way ticket is 20-25 euros). You can get acquainted with the timetable and buy a ticket via the Internet.