Peter gave them a full account means that Peter told them “point by point” what had happened (see Jerusalem Bible “gave them the details point by point”). A full account of what had happened may be equivalent to “everything that had happened.”

From the very beginning may need to be somewhat more specific in some languages, for example, “he began talking about what had happened first” or “he started with the very first thing that happened.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on The Acts of the Apostles. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .