Web conferencing has more features than a simpler video call. There are many features that you can consider teaching your participants. Some may be the focus on your one pager for this section. Not every participant will be interested in every feature. You will need to "read the room" as you are working with people to see how much or how little to help them with.
Consider showcasing the following functions.
Give a complete tour of the main buttons like Mute, Video on/off, and Leave or End meeting.
It is helpful for people to know how to mute and unmute their microphone. They should mute their microphone when the room becomes noisier. They may want to mute when they need to cough or talk to someone else in their room. It's so common that people forget they are muted that it has become somewhat of a joke about web conferencing. Show them the indicator for when they are or are not muted, and try to be patient if they continue talking while being muted.
Be sure people know how to adjust the volume of their speakers. They may need to be reminded. Suggest using headset or earbuds for better sound quality in noisy environments, if they are available. The headset or earbuds they use should also include a microphone or shouldn't cancel out using the microphone on their device. Usually they won't be in a room full of people when they are web conferencing with loved ones.
The main purpose of web conferencing is to share video, but there may be times when it's acceptable to turn it off. Most people won't likely do this while web conferencing with a friend or loved one. In other situations, it may be appropriate to turn off the video. This may include when you have to leave the room for a little while or when you're an observer in a large session where your input isn't necessary, like watching a webinar or lecture.
For many people, chatting through video and audio is enough. Most web conferencing applications do support text chatting, however. This can be helpful when trying to share information that is hard to understand by audio. Maybe during a web conference with a financial planner, the planner can share an important website URL or email address. Some chat features also allow people to share documents.
Apps like Zoom allow you to change or modify your background in your video. Your participants may want to know how to blur their background for some people if they are in their bedroom or in a distracting setting. It can be fun to play with some of the virtual backgrounds and filters. They might invite their grandkids to connect on another planet or from a different city.
Some web conferencing applications will include Closed Captioning, translation, and transcription services. The settings for these and other features can be adjusted under the Settings for the application you are using. These features may not be available in all applications.
Review these two articles on specific webconferencing applications.
There may be other features that can be found in web-conferencing apps, but this list is probably longer than you'll need. Most adults will want basic information so they can use web conferencing to connect with family and friends. Some may need it for support connecting with a financial, medical, or other professional. Try to talk to some older adults to see how they might use web conferencing. It's possible they can give you a topic specific enough to create your one pager for this section.