Rapport is the result of having been mirroring the experience of your partners back to them so that they can see themselves in you and feel safe. Mirroring is the useful matching of your partner's vocal tone, the key words they use to convey their meaning, and the body language they use to express themselves fully. The skills of mirroring and matching can be learned by everyone. The benefits of rapport are trust, connection, and alignment that has been authentically earned.
Try this the next time you're talking someone on a break. Notice their body language (crossed legs, folded arms, posture), notice their word choices (concrete terms, general concepts, sensory details), and notice how they speak (short phrases, long stories, tonality). Pick a couple of these details to mirror back to them and do the same thing they do. The mismatch your mirror and do the opposite of that they're doing. See what difference, if any, you notice in the person you're talking with and in yourself.
Chances are, your conversation will flow better when you are in rapport than when you are out of rapport. When we are in rapport with someone, we are sending a message to that part of their brain that is sorting for survival-level that we are just like them--that they are with "like kind", part of the tribe, safe. (Of course, there are people you'll meet for whom being "safe" is the most dangerous state to be in, but that's a topic for later.)
So now that we have rapport with someone, what can you do? The benefit of being in rapport with someone is that your ideas, stories, and offerings to them can begin to be accepted more easily. Just like it's easier to put a letter in an envelope if the envelope is open. Rapport sends the message to the envelope that it can open on its own--and that what will go into the envelope comes from a trusted source.
But the act of getting into rapport isn't only about you doing something to someone else. It's mostly about you getting yourself into alignment with someone else's experience and map of reality. It's about you giving yourself permission to be aware of someone else's differences and bringing yourself into alignment with those differences. And from that place of allowing others to be as they are, and you to be as you are, the whole interaction can take a breath and settle into something remarkable and freshly authentic.