Fediverse

Tell them it's like Twitter, reddit, Instagram, and YouTube all in one. You can sign up for whatever type of content you want, just like you would sign up for any of those aforementioned sites, but the difference is that the sites can all communicate with each, and are independently run by non-profits, community groups, and different organizations and individuals, rather than a single centralized entity. You can select an instance of the software that suits various interests or niches, or just join a large instance for a bigger pool of content to start with locally. No wrong choice, as even small instances can communicate with large ones, just pick one you like and suits your values or convenience.