And we also thank God constantly for this, that when you received the word of God, which you heard from us, you accepted it not as the word of men but as what it really is, the word of God, which is at work in you believers. (1 Thessalonians 2:13 - ESV)
There are two things that they do when they hear the word... but the fact that they heard the word implies a couple of things already. First it implies that it is being spoken. The Gospel is being shared verbally. Second it implies that they were listening.
Now that they have heard the "Heard Word of God," there are two things that happen. Number One: It is received. This word (received) goes beyond simple hearing. It is the word that is often used in Greek literature for a student taking in what their teacher is teaching. They were listening, hearing, and it was being taken in! There was mental computation happening. Thought processes were being incorporated. World views adjusted. Sights shifted.
Number Two: It is accepted. One commentator, Gene Green, says, "… while accepted is almost synonymous with received… the verb commonly places more emphasis on personal appropriation.
… in other words… they solemnly received the sacred message and appropriated it for themselves." But "appropriated"? Think of funds that are appropriated for a budgeted purpose. They are clarified for that specific use. This means… When they accepted the word (that they had heard and received), they began to incorporate it into their lives. They would set it aside for use. Their thinking. Their living. Their decisions. As in, "Oh. that would be useful there. That would go here." The word of God specified for a specific use.
This has poor video quality, but here is a sermon on this verse: