'yiw' is yank inner word. It basically copies the current word from wherever you are in that word. The pure yank 'y' I presume would just work if you already have something highlighted. It looks like these shortcuts take the current word or current selection and pass it to Rg [0] to be searched for.

I don't have the plugin but it sounds super useful and I'm going to give them a try.

[0] Rg being ripgrep, see https://github.com/BurntSushi/ripgrep