What does he mean by "the deep end"?

Native speaker’s answer
Rebecca
Here, "the deep end" has a couple of meanings. In the context of working at a swimming pool, "the deep end" is the part of the pool that is very deep, and you can't stand. As a phrase, if someone is "thrown into the deep end", it means they are in a completely new situation. They are not prepared, and they don't know what's going to happen. So for him, this is his first time as a lifeguard, so he's in "the deep end" as this is a new situation and challenge for him! Ex: I was thrown into the deep end when I said yes to helping with this project. I've never done coding before! Ex: I prefer the shallow side of the pool where I can stand rather than the deep end. Ex: When the company fired him, he wasn't afraid to jump into the deep end and start a new business.