This is one of my rear occasions to ask a question. I don't have any
idea what to search for to try to figure it out.

I did not create this. I have no idea how this works or what key
strokes trigger it. Can someone help me understand how to use it? It
looks like there are two or three mappings below. Does it go in the
.vimrc or somewhere else?

" Search for selected text, forwards or backwards.
vnoremap <silent> * :<C-U>
  \let old_reg=getreg('"')<Bar>let old_regtype=getregtype('"')<CR>
  \gvy/<C-R><C-R>=substitute(
  \escape(@", '/\.*$^~['), '\_s\+', '\\_s\\+', 'g')<CR><CR>
  \gV:call setreg('"', old_reg, old_regtype)<CR>
vnoremap <silent> # :<C-U>
  \let old_reg=getreg('"')<Bar>let old_regtype=getregtype('"')<CR>
  \gvy?<C-R><C-R>=substitute(
  \escape(@", '?\.*$^~['), '\_s\+', '\\_s\\+', 'g')<CR><CR>
  \gV:call setreg('"', old_reg, old_regtype)<CR>

" Convert curly quotes to straight.
" Any argument causes substitute to confirm changes.
function! ToStraight(line1, line2, args)
 let flags = 'eg'
 let range = a:line1 . ',' . a:line2
 if empty(a:args)
   let range = 'silent ' . range
 else
   let flags .= 'c'
 endif
 let search = @/
 exe range . "s/['']/'/" . flags
 exe range . 's/[""]/"/' . flags
 nohl
 let @/ = search
endfunction
command! -nargs=? -range ToStraight call ToStraight(<line1>, <line2>, '<args>')

Thanks for the help,
Jack