Hi!
To reiterate, it’s not you. The learning curve on the repeater is steep withn a product whose learning curve is steep. I’ve used repeaters daily for years, and I still find tricks that surprise me.
I wrote a Medium article on the repeater a while back. The primary focus is how powerful OnItemLoad (or whatever it’s called now) can be, and it includes an introduction to expressions and repeater item properties. Without understanding what exactly happens during OnItemLoad, fully understanding the repeater is impossible.
Filtering is a topic of its own, and is vastly powerful. And there’s a topic that deals with accessing/manipulating the repeater from outside of the repeater called “the listener method,” which you pretty much have to Google. When I’m not on my phone, I’ll post some forum links.