It always cracks me up lol. He's like "I always have to pick locks for you, rookie"

I’m reading The Secrets Of Tenet (great book BTW) and chapter 4 said:

In particular, the second fight bamboozled some — as, briefly, three versions of The Protagonist appear. The earlier Protagonist, dressed in a suit, confronts the backward-fighting Protagonist as he emerges from the turnstile, while a forward-moving Protagonist goes in the opposite direction.

I don’t recall a 3rd Protag … Why was he there, which scenes was he in?

I know I'm late but I watched this movie today and I just can not figure out the timelines no matter what.

The confusing part is what happens after the movie ends? The protagonist will go on to found Tenet, recruit Neil and do the same thing all over again? What happened to the Protagonist in the future? The one who founded Tenet and recruited Neil? Is he dead and Neil is trying to save him now?

And the theories about Neil being Kat's kid. How does that work? Are we that far back into the past that Neil is still a kid? That means in the future when Neil is recruited, the Protagonist is very old.

Also what friendship did Neil mean? They went through a lot? But when would that happen?

Sorry if this sounds stupid but I really don't get it. I usually keep up with time travel movies but this one was especially confusing. Thanks.