There are several bus/train stations in Szczecin. Before buying online tickets, check the map below in order to choose the stop that is closest to the city centre.

Szczecin-Goleniów airport (SZZ), ca. 40 km from Szczecin >>>  shuttle bus service and train connections to the city centre;
Warszawa – Chopin Airport (WAW), ca 520 km from Szczecin >>>  direct train to Szczecin;
Berlin Brandenburg airport (BER), ca 150 km from Szczecin >>>  direct shuttle bus service to Szczecin.
The most common shuttle bus services:
Interglobus
FlixBus
PKS Szczecin

The arrival station: SZCZECIN GŁÓWNY (the main station, Hbf). Polish Railways >>>
The main station serves direct train connections with all major Polish cities: Warszawa, Kraków, Poznań, Wrocław, Gdańsk, etc. There are several connections to Szczecin-Goleniów airport (Port Lotniczy Szczecin-Goleniów) as well.
You can reach Szczecin by international direct and indirect regional trains from Berlin, Greifswald, Lübeck, Rostock, etc.

You can arrive to szczecin by international coach service as well. The main coach station is at 1, pl. Grodnicki in Szczecin. You may check the connections here https://en.e-podroznik.pl/

Check how to arrive to Szczecin by car  >>>
You may use BlaBlaCar to share the cost of the travel and reduce your carbon footprint.

The closest ferry terminal is in Świnoujście that serves connections with German and Scandinavian ports. It is about 1,5 h from Świnoujscie to Szczecin by car or train.
Polferries
Unity Line
TT-Line