Okay kiddo, imagine you have a big jar of candy. You want to share it with your friends, but you don't know if they want any. So, you say "if my friends want candy, they can take some!" That's an example of subjunctive possibility.
Subjunctive possibility is when we talk about something that might happen, but we're not sure if it will actually happen. We use words like "if" or "might" to show that it's not a sure thing.
For instance, if you say "If it rains tomorrow, we might stay inside," you're using subjunctive possibility. You're not sure if it will rain, and you're not sure if you'll stay inside, but you're talking about the possibility.
Subjunctive possibility is also used when we talk about things that we wish were true, but aren't. For example, you might say "If only unicorns were real, I would ride one to school!" Again, you're using "if" to talk about something that isn't actually true, but you wish it were.
So, kiddo, that's what subjunctive possibility is. It's a way of talking about things that might happen, or things that we wish were true, but aren't sure about. Pretty cool, huh?