[TYPO3-dev] What is settings in extension manager for?

[Rayuth You]

Hi all

I am a newbie typo3 and try to look through typo3 back-end.
I go to extension manager and in drop down menu I choose settings.

Could you tell me or give me the link what settings is for?
Because I can not find document relate to this, even I tried in google.
Most of document I found is talk about extension manager, install 
extension, import extension but no settings. So I do not know what 
settings is for?

Thanks,
Rayuth