Albert Barnes on Acts 8:17

Then laid they their hands, etc. This was an act of prayer, expressing an invocation to God that he would impart the blessing to them. On how many they laid their hands is not said. It is evident that it was not on all, for they did not thus lay hands on Simon. Perhaps i.t was done on a few of the more prominent and leading persons, who were to be employed particularly in bearing witness to the truth of the gospel. It was customary to lay the hands on any person when a favour was to be conferred, or a blessing imparted. Mt 9:18.

(c) "laid they their hands" Acts 6:5, Heb 6:2 (+) "Holy Ghost" "Holy Spirit"