Hello @hari3435 - I'm not able to answer all of your questions but I'll help where I can. First I will say that there are plenty of videos and resources online that describe how to produce a live event.
how can I change both presenter and my own webcam video during events ? If you are the owner or producer, you can switch the presenters and their content in the queue before sending the image live to the audience.
please describe in details . and immediately i have events today 8 pm.
2) some meetings do not allow people to join as guests . what is this ??? You need to set your settings to allow public attendance and then send the attendance link to whomever you want to invite.