What is Being? As I interpret the topic, it's to try to give an account of lived "reality", in such a manner that what is taken for granted can be seen as a stupendous achievement of human beings capacity to order and structure this world.
What we take to be a simple rock depends on many factors, including language, social convention, perception, categorization, recurrence of experience on the same object and so on. We can, for instance, isolate as aspect of the rock, say it's grey colour (qualia) and somehow conclude that the colour is not fundamental to the existence of a rock.
Likewise, we predict this never before seen object, a rock, based on previous examples found in similar situations in which, based on our experience with such objects, we are able to conclude that this other object is a rock too. What's included? A certain texture, a consistency of the object, its location in our environment (it would be strange, but not impossible, to find a rock on top of a flower, for instance) as well as our use of it.
Do we use rocks as decorations, weapons and so on. If we have no conceivable use for an object, we probably could not categorize it as anything.
This can be thought of in the framework of "disclosure of being", or analyzing what's in "the given of experience" or consider that it is a construction of several categories, such as Peirce thinks it is. And so on, depending on which author you tend to think is on the right track.
That's the rough idea.