Zoom is an online video conferencing platform, see https://zoom.us.
To use it you’ll need a phone, tablet, laptop or desktop with a microphone and webcam. If you want to improve the quality of your video and audio, you may wish to buy separate webcam and microphone components from manufacturers such as Logitech or Blue.
If you want to join a meeting, you need only download the app, you do not need to sign up for an account. Click on the meeting link sent to you by your host and the relevant app will automatically be installed. If you’d like to download it in advance or on several devices, go to https://launcher.zoom.us/download.
If you want to host a meeting, you must sign up for a package. The basic package is free, but has a limit of 40 minutes for groups. You can stop and start a new meeting to extend your time. The next level up (Pro) has a monthly or annual fee and permits group meetings of up to 24 hours. Both allow up to 100 participants. Check the Zoom website for current plans and pricing.
As the host, it is up to you to start a meeting, then invite participants to join you by sending them the meeting link. You have more controls than the other attendees and there are quite a few options that you can manage during the meeting or pre-set.
There’s plenty of online help, see: