In vim doc, use Ctrl-] to jump to the tag under the cursor,
use Ctrl-o to jump back.
For example, run :h airline (you must have installed vim-airline,
see note "Customize Vim Statusline" for details).
Put the cursor on "airline-customization" in section "CONTENTS",
press Ctrl-] to jump to section "CUSTOMIZATION",
press Ctrl-o to jump back to section "CONTENTS".