What does "reset all settings" do and what do I need to do after? I have an iPhone 6 with an IOS 9.3.2 update

Settings>General>Reset>Reset all settings.

IF you look what is in the settings app, you will have to re-enter/redo everything that you have set up in the app. You will have to rejoin all WiFi networks again, re-enter all passwords, set all of your privacy settings, your preferred wallpaper, select ringtones, reset notifications, and so on. Basically, whatever is in the settings app will have to be re-entered.

Your phone will also reboot on its own when you reset all settings. It takes some time to get everything back to where you had it, but it's not so bad. I have done it a few times.

Erase All Content and Reset all settings removes everything except the iOS from your phone and starts you over.

The restore using iTunes removes the iOS, replaces it with the most current copy and then removes all content and starts you over.

Reset All Settings removes a number of items stored in volatile memory, but no user content or the iOS.

Similar but different.

If the issue affecting your device is within the iOS, the reset all settings or erase all content and settings won't resolve it.

Did you reset all of the settings? What that does is return the device to Out of the box, default settings. All of the settings are returned to what they were when you first activated the device - before you made any changes on your own.

They suggested resetting all of the settings on the assumption that one of your settings was corrupt.

Ok. Good luck. If you need more help, post back.