On the Fish Deeper App and many other sonar displays the data on screen is shown scrolling from right to left. The far right of the display shows the most recent results, the oldest are on the left. You should remember that your screen will keep scrolling even if your sonar isn’t moving, because the unit is constantly sending and receiving sound pulses. Understanding how this scrolling display works is really important for making sense of the sonar data you receive.
You can learn more about how sonars work here.