It tells us to observe specific traditions; i.e., those learned from Paul.
2Th 3:6 Now we command you, brethren, in the name of our Lord Jesus Christ, that ye withdraw yourselves from every brother that walketh disorderly, and not after the tradition which he received of us. 2Th 2:15 Therefore *, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.
This does not say that we are to accept any old tradition that happens to come down the pike. It says that it has to come from Paul.
Since the Thess letter was penned in the neighborhood of the early 50's AD, and since Jesus was crucified in ca. 33 AD, we are talking about an entire 17-20 years of teachings and practices that were handed down. Since Acts was written later than Thessalonians, as were other letters, we can be assurred that we have the entirety of necessary traditions from those 20 years included in later books.