Nod
Greeting, Bow
noun, する verb
Before you can give an explanation of who you are to someone you're about to meet, you have to nod or bow as a greeting first. It's rude to start explaining who you are before you greet them.
えしゃく
This is a jukugo word that uses the on'yomi readings of the kanji. You didn't learn this reading for 会 yet, so here's a mnemonic to help you:
When someone bows to you, you always feel a little uncomfortable, so you say, "Eh" (え) and try to get them to stop. You're so uncomfortable that you can't think of words and "eh" is all you can manage to get out.
会釈をしたら会釈を返すのが礼儀でしょう。
You might have the decency to return my nod with a nod.