What Tradition is Paul referring to when he admonishes us to "hold the traditions which ye have been taught"?

For those who do not agree with Sola Scriptura, which is scripture alone is the source for all things pertaining to your salvation, they often quote this from Paul. Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle. 2 Thes 2:15 For them, this is their proof text that you should hold Traditions as salvific. To what specific "traditions" actually extant in Paul's time is he speaking? Are they the four Marian dogmas? Are they the filioque? Are they Peter's successors are the head of the church? Exactly what are they? How do you know? If one doesn't know, why would someone place their trust in them for their salvation?