Easiest method to get to the venue is to Uber your way there.
If you prefer existing public transportation, the closest train and metro station is S. Bento; You can then catch the 500 Matosinhos (Mercado) STCP Bus at S.Bento (SBNT1) down to the Alfândega Stop (ALFG1) (4 stops, 6min). You’ll need the Andante rechargeable card with 1 Z2 trip loaded (1,20€) or buy one ticket on board (2€).
When moving around the city, we recommend choosing the subway first, uber second and taxis third. Lime scooters are also an option. Porto is walkable (and you get to see more of it that way) but do keep in mind that it is full of hills. It’s mostly downhill to the venue.
If coming from the airport, the “E” metro line has service about every half hour. This line takes 26min to get to the city center (Trindade stop). However, the subway option at the airport isn't as good as it could be, if you need to get into the city's center. Uber (~15€, estimated without possible surge prices) or taxi is a better / faster bet. Also, the city is full of stone sidewalks ("calçada") which isn't great for rolling a suitcase around.
You can use STCP Site or Moovit to check the best available public transport options, cost, and type of ticket you need to buy to get from A to B. Also, here you can find all the tariffs available if you are considering moving around using public transportation
You can also check out more info on the Metro website. Subway and bus usage requires a rechargeable card (Andante card) that you can acquire at the station (0.60€) and add any number of trips that can be used both on the metro and STCP buses