Presence information is a way to let people know if you are available or not. Imagine you are playing with your toys and your mom wants to know if you are free to eat lunch. She might look at your playroom door and see that it is closed, which means you are not available. But if the door is open, she knows you are free to talk and eat.
The same thing happens with technology, like phones or computers. There is software that can show people if you are online and available to chat or not. This software might change your status from "available" to "away" or "busy."
This can be helpful because it lets people know if they should try to contact you or not. It's like a little signal that says "hey, this person might not be able to answer right now, so don't get upset if they don't reply right away."
But it's also important to remember that just because someone's status says they are available, it doesn't mean they are obligated to respond right away. They might still be busy doing something else or simply not wanting to chat. So it's always good to be respectful of others' time and boundaries.