Depends on your audience and what you want to emphasize. Whenever I talk about iNat, I personally always stress the community part, especially for people unfamiliar with it. I know there is so much more as well, but there are plenty of other apps that can help identify plants and animals, using AI. To me, the community part of iNaturalist helps it stand out.
So I call it “a community for nature-lovers” first and add on. It’s also easier for the typical person to grasp and might pique their curiosity, leading them to ask more questions and allowing me to get into more detail.
“In essence, it’s a community for nature-lovers, where people post and help identify photos of plants and animals. Social media for naturalists.”
If you want to emphasize the impact/contributions part, you could say: “It’s a community of nature-enthusiasts who create and manage a worldwide database of nature observations that can be used for research.”
With your audience:
I think it’s better to start general, but if at all possible do what @ItsMeLucy said:
Words only get so far. Show the app. Better yet, pull up the web version and a map! Pull up the observation of the then-lost (and now refound) Dumbea River Pipefish and quickly discuss its story, or the one with Gonolobus naturalistae! People like to look at maps or images, and better yet hear stories. Now that I think about it, I think I’d prefer a “show rather than tell” method, if at all possible.