Google Nexus 5 - Customise your favourites tray

At the bottom of each homescreen is your favourites tray, which consists of 5 icons. You can customise it by adding icons to the tray. If it’s full however, you will first need to remove some.

To remove an icon, simply press and hold an icon. Then drag it to your desktop.

Then to add a new one, simply drag an icon from your homescreen to the favourites tray.