Brain hurts… focus keyword help please

I’ve just started using Yoast (after learning my old SEO plugin was not working hence none of my meta data was showing. yikes)
I’m pretty brain fried from all the info and I wondered if someone might clarify just a bit on this topic. I’m sure the info is “out there” somewhere but I just can’t pin it down and I’m exhausted from this stuff.

So, there is no multiple keywords now… which I understand. And only ONE focus keyword. And we need to use long tail keywords… though that sentence seems to always be plural in your tutorials if we’re only doing ONE focus keyword I assume that means “one long-tailed focus keyword”… correct?

(I’m struggling with the just one thing only because some posts have two or three VERY strong purposes. )

So to clarity… I need ONE long-tailed keyword basically that sums up my post. (After researching it out as best I can.( Correct? And I just assume the other important key topics in my post will… what… get found anyway?

Like I said… my brain hurts…

Nancy

https://wordpress.org/plugins/wordpress-seo/