What is Play mode vs Build Mode?
What is the Move Tool?
What is the Arrow Tool?
The Arrow Tool is intended to help you point at sticky notes during discussion. If you are talking with your team in the same room or over voice/video conference you can use the Arrow Tool to point at the Post-it you are discussing. The arrow points at the position you start dragging from so that you can "wiggle" the mouse around if needed to draw attention but keep pointing at the same object.
The arrows are only temporary, they will disappear as soon as you click somewhere else or change tool.