in this line:
nnoremap <C-L> :nohl<CR><C-L>
nnoremap
means normal no-recursive map <C-L>...
which means, if you press ctrl + l
in NORMAL
mode, the mapped key-strokes would be applied.
<C-L>
means ctrl + l
if you type
:h control
you can see the keycodes:
<C-...> control-key *control* *ctrl* *<C-*