Go to the "Font" tab of a style, e.g. character style or direct formatting. You will find a button "Features..". It opens the new "Font Features" dialog. Dependent on the selected font, you will find only few or a large amount of settings. Try font "Linux Libertine G" for example. A help for that dialog is missing.
And since version 5.3 you can add such feature to the font name, e.g. "Linux Libertine G:liga". The help for that is missing too.
I think, that there should be a common help page on OpenType features, which describe, how and where such features are supported in LibreOffice. The page need not explain each OpenType feature, but should help the user to find such information, perhaps providing suitable search terms and links to the standards. And it should show the effect of these features on some examples.
Such help page should be indexed with "OpenType".
*** Bug 121306 has been marked as a duplicate of this bug. ***
Olivier Hallot committed a patch related to this issue.
It has been pushed to "master":
tdf#119269 Font Features Help page
A polite ping to Olivier Hallot:
Is this bug fixed? if so, could you please close it as RESOLVED FIXED ? Otherwise, Could you please explain what's missing?
(In reply to Xisco Faulí from comment #3)
> A polite ping to Olivier Hallot:
> Is this bug fixed? if so, could you please close it as RESOLVED FIXED ?
> Otherwise, Could you please explain what's missing?
I see a help page in Version: 22.214.171.124.alpha1+ (x64)
Build ID: 115ab48f86d4e3c6eede49767df1ee5a82b4ab22
CPU threads: 8; OS: Windows 10.0; UI render: default; VCL: win;
TinderBox: Win-x86_64@62-TDF, Branch:master, Time: 2019-05-20_17:50:30
Locale: de-DE (en_US); UI-Language: en-US
and a click on the Help button in the Font Features dialog opens this help page. So for me the bug is fixed.