English Other Telecom(munications) videoconferencing

what is the meaning of "to acknowledge" here?
When the Videoconference Begins
Welcome the participants when all sites have been connected. Always begin with a roll call for all sites
to acquaint participants with speaking in the videoconferencing setting and introduce them to one
another. If you don't already know everyone, make a seating chart of remote sites with people's
names as they introduce themselves. This will help you to call on participants by name when they
have a question or you want to acknowledge them.
Tell participants how to respond to or ask questions. You may want them to state their name and
location before they begin or simply raise their hand when they have a question so you can give them
a chance to speak. Next, review the meeting agenda, objectives, breaks and end-time as well as any
materials sent to participants prior to the meeting.