For heading south (to Warsaw or small villages in between for eg)
Go to the intersection of Ul. Tuwima and Ul. Warszawaska. it is right next to Kortowo (the university campus). From there, u will see a bus stop 10m further south from the intersection on Ul. Warszawaska. I havn't tried on my own, but when i was waiting the local bus there, i often saw people hitchhiking there (and got picked up of course).