If you want to check LATEX documents: Add let g:coc_filetype_map = {'tex': 'latex'} to ~/.vimrc (Vim) or ~/.config/nvim/init.vim (workaround for #425, until neoclide/coc.nvim#3433 is released)
Open a LATEX or a Markdown document
Wait until ltex-ls has been downloaded and started
Grammar/spelling errors will be displayed! (if there are any)