If the Home button is damaged and no longer working on your device, turn on this option to enable a virtual one. From the Accessibility menu in Settings, tap Touch and then turn on the AssistiveTouch option. A white dot will appear on screen. Tap this to access popular options such as the Home button.
The dot fades after a few seconds so that you can see through it, but tapping on it will wake it up and reveal the options again.