via (https://www.linux.com/learn/tutorials/442438-vim-tips-folding-fun)
za
toggle a fold at the cursor (zo/zc)zA
toggle all folds at the cursor (zO/zC)zm
increases the foldlevel by one.zM
closes all open folds.zr
decreases the foldlevel by one.zR
decreases the foldlevel to zero -- all folds will be open.zj
moves the cursor to the next fold.zk
moves the cursor to the previous fold.zf#j
creates a fold from the cursor down # lines.