Heidegger has the notion of "the they" in his characterization of Dasein. The characterization of Dasein is a characterization of one being receptive to the norms of what one does. It is a matter of being attentive to whatever the customary modes of behaving are. Who you are in your everyday activity is whoever one is when one is walking around comporting oneself. It is Dasein as receptive -- as already in all of the normal and usual active involvements in activities that hold their meaning in virtue of the social norms for what one does in those kinds of activities. As such, it is the case that we already find ourselves in a world that we are open, sensitive, and responsive to in terms of the social norms of what one does in whatever situation in which we find ourselves.
Heidegger then gets into the issue of authenticity or mine-ness. Think of this as "owning" the situation. Somebody is in the mode of authenticity when they are "owning" whatever it is they stand for in the world. Most of the time Dasein is not disclosing itself authentically. However, what somebody does normally and usually, that is, what somebody is used to, pertains to the condition of the possibility of doing something that is authentic. This relates again to the ontological difference between veiling and revealing. To be authentic is not a matter of taking myself present-at-hand (revealed) but it is more a matter of who I am when I'm going about doing the things I'm used to. It's being myself and doing what I do accordingly. I can "own it" most naturally when I am involved in the activities I normally and usually find myself involved in. That's when I can authentically stand for what matters to me. Somebody doesn't calculate and formulate their authenticity. Somebody becomes authentic. They gather themselves authentically.