Q: how to hide setting app on ios 9 ipad mini

You cannot hide the Settings app.  The iPad is supposed to be for one user, and that user needs access to Settings.

If you are giving the iPad to a child to use, this can keep the child out of Settings:

Use Guided Access with iPhone, iPad, and iPod touch - Apple Support

The closest you can come to hiding it is to put it into a folder and tuck it away on a back menu page. To put an icon into a folder, hold your finger down on it until it starts to wiggle. Then drag it over another icon (to be in a folder there must be two items). They should create and drop into the folder. You can single tap the home button to exit the mode.

If you're wanting to hid it to prevent changes, you may want to poke around in the restrictions and see if you can lock out the changes you don't want made. Settings, general, restrictions. You'll be promoted to make a 4 diget pass code, do not forget this number because the only way out if you do forget it is to wipe your device clean. Then see if you have the ability to lock out whatever changes you don't want made.