It may be a bit hashy because I’m still in the early stages of understanding it myself but I’ll give it a go.
I won’t do a Heidegger on you and put the answer before the getting to the answer so I’ll paste here what was going to be my last paragraph:
“It is Care (Giving a damn) that distinguishes Daseins from things that are objectively present like stones. It is because Dasein gives a damn that it acts or doesn’t act.”
Dasein is that which discloses things in many ways. By disclosing Heidegger means revealing.
So Dasein as being-in-the-world discloses a world.
Equiprimordial with Being-in-the-world is Being-the-there. In a sense you could say that Dasein discloses a world in which space (the-there) can be.
Dasein also discloses by understanding; but Heidegger doesn’t use understanding in the normal sense of the word. By understanding Heidegger means that Dasein realizes its possibilities of Being. That is to say Dasein realizes it could engage or not engage in certain activities.
In the act of understanding Dasein projects itself onto those possibilities. “I could be a juggler, carpenter, banker or whatever”
In fact understanding is a possibility of Dasein’s being: Dasein as understanding.
From understanding Heidegger derives interpretation. The Dasein understands the possibility of juggling and understands 3 possibilities.
To engage in the activity of juggling.
Not to juggle
To enter into the possibility of interpretation which would ask “What are these handy things I juggle with?” “What is juggling?”.
He then talks of Dasein as attunement.
I think he means understanding is a kind of attunement as well but I’m not sure.
He says that attunements are kinds of moods; but again I don’t think he just means emotional moods because he says before we are able to feel anything (like a table) we have to have the existential of attunement. I think he is saying something like attunement is the capacity to feel anything included via the senses.
He then talks about thrownness.
How Dasein is thrown into a situation and is normally entangled in the They. That is to say that Dasein in this mode has its understanding limited by the they.
The they (as I see them) are culture, society, others, or any gathering of people with shared social norms.
So for example the Dasein in the current social milieu if he is entangled in the They would understand the possible beings it could be to be banker, cleaner, or anything socially acceptable; but wouldn’t realize the possible being of going into the forest and living like an animal.
I think the simplest and best definition of Dasein Heidegger gives is that of care. Dasein is a being that cares about its own being. Now you cannot derive Dasein by a putting together of all those equiprimordial existential features but must see those features through the whole of Dasein.
Now understanding, modes of attunement – such as anxiety – interpretation and activities Heidegger says derive from Care. So Heidegger says that care is the most primordial feature of Dasein.
Not care in the particular sense of “caring for something” which is derived from this Care. But the care one has for oneself and ones potentialities and possibilities of being.
It is Care (Giving a damn) that distinguishes Daseins from things that are objectively present like stones. It is because Dasein gives a damn that it acts or doesn’t act.
So according to my first reading; first incomplete reading that is (I’m only on chapter 6) that last paragraph is the simplest and clearest definition of Dasein I can give.
Hope you found it helpful.