Assistive Touch is a known feature in iOS devices which gives you a quick touch access to some system settings. and this feature has been recently added Android devices by default. To enable Assistive Touch on LG G4, do as follows:
1. Open the Settings app and make sure the List View is enabled (If not, tap the 3dot icon on the top right and touch the List View option)
2. Scroll all the way down to System settings and tap the Accessibility option
3. Under the Type settings, tap to open the Motor & Cognition menu
4. Now, under the Motor settings, make sure the Touch assistant toggle button in On
5. A small floating touch button should now appear on the screen, and tapping on it gives you quick access to: Adjust the volume, Go to home screen, Open the Power menu (To Power off, Restart or Turn on Airplane mode), Capture the screen, Pinch to zoom in/out and launching some applications by drawing their initials*
* Regarding the draw to launch, for example if you draw a "C", then the "Call" app will launch. (If you touch the Touch assistant text field, you get to see the other supported app for quick launch)