to recount in detail, to relate what happened
This is the plain, everyday sense of the word, and it covers five of its six appearances in the New Testament, all of them in Luke and Acts. Someone has witnessed or experienced something and now sets it out for others, point by point, the way you would give a full account of a trip or report back on a meeting.
The stress falls on telling the whole story, not just mentioning it. When Paul reports to the leaders in Jerusalem, the text says he went through what God had done item by item. The word fits formal testimony as comfortably as ordinary conversation: the same verb describes two travelers swapping news on a road and apostles giving sworn testimony before a council.