via (https://www.linux.com/learn/tutorials/442438-vim-tips-folding-fun)

• zf#j creates a fold from the cursor down # lines.
• zf/string creates a fold from the cursor to string .
• zj moves the cursor to the next fold.
• zk moves the cursor to the previous fold.
• zo opens a fold at the cursor.
• zO opens all folds at the cursor.
• zm increases the foldlevel by one.
• zM closes all open folds.