To access the build menu, walk west in your cult's area until you reach the sign with a hammer on it. (shown below). You can open this menu in multiple ways, like clicking on it with your mouse or pressing "E" on your keyboard.

To open the edit mode, look towards the bottom-left hand side of your screen, and press the displayed bind. ("C" by default on keyboard.)

Once inside the editing mode, a hammer will appear in the center of your screen. To move the hammer, you simply press the W A S and D keys (keyboard and mouse), or by moving the left joystick (controller).

You can select a building by simply hovering over it with your hammer. This will display three options: "Move", "Remove", & "Cancel". (Note: some buildings cannot be removed, like the Temple.)

This mechanic took me 30 minutes to find, so I figured I would write a super quick guide for those, like me, who could use it. This is my first Steam guide, so it isn't perfect whatsoever.