Hey, sorry that I didn't really try to explain the bindings. Climb_stealth said it all really but here are some extra bits.
The first one is a normal mode binding (the n in nnoremap). yiw copies the word you are currently on (without surrounding spaces), and then <C-r>" pastes that into the :Rg command. The :Rg command is part of the fzf vim plugin and it is a wrapper around ripgrep (see the link from climb_stealth), which gives you fuzzy search over the results of a ripgrep search.
It's basically just how you paste the contents of registers into commands.
The second one is almost exactly the same except that it is a visual mode mapping (the v in vnoremap). If you highlight something with visual mode, then use that command, it will search for the highlighted text using ripgrep.
<C-Space> is just the key chord that the command is bound to. It is a pretty arbitrary personal choice, I find it a very quick and easy chord combination but you can put whatever you want in there. For example, <C-S> would activate the command when you pressed the chord 'control + s'.
There is quite a good list of keys that are unused by vim here:
'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.
