I saw that there's already a question about this but the emphasis was on what could being be if not an entity. Heidegger thinks of Being as something "extra", a priori, to entities. I'd like to question the "need" to make such a differentiation between entity and being.
Heidegger makes a (difficult) distinction between 'beings' — entities that exist in the world, like tables, papayas, or wombats — and 'Being,' which is the activity of existing. This is a noun/verb distinction: just as you have 'runners' and 'running,' where the former are entities that are defined by the latter activity, so we have 'beings' that are entities defined by the activity of 'Being.' 'Being' is not itself an entity; it is the condition by which something is classified as an entity.
Being is not something extra to beings. Instead, beings are specific instantiations of the general principle of Being.
Heidegger makes this distinction because he wants to get at the nature of this activity of being-ness without getting bogged down in specific examples of being-ness (i.e., entities). In fact, Heidegger thinks that the focus on entities obscures the question of Being. If we look at a table, we tend to start at the premise "that table exists," and lose track of what Heidegger thinks is the important question: what activity is that table engaged in that means it exists? We need this conceptual division or we will collapse into a kind of reductionism (a mere list of particular beings, not an understanding of the nature of Being itself).