The panel editor which you use to create a panel is described on a separate help page.
This control can be used in various ways. For example, you could have a turnout icon covering a turnout on a schematic diagram. When you click on it, the turnout on the layout would be commanded to change, and the track diagram would show which way a train would be routed. Or you could use icons that show a lever to the right or left, and create a panel that looks like a traditional US&S panel.
"Sensors" can be used to represent occupancy indicators or other inputs. The default icon is a small circle, with color used to represent the state of the sensor. These respond to changes on the layout automatically. Clicking on a sensor causes the sensor to alternate between "active" and "inactive" states. With the default icons, active is a green circle and inactive is an empty circle. These are meant to represent a lit/dark panel indicator. A red circle represents the "unknown" state, used when no information has yet been received from the layout.
If enabled via the checkboxes on the Panel Editor, you can move an icon by dragging it around the panel. For more precise positioning, many icons can access the Coordinate Editor to move the icon by a specific number of pixels or set it to an absolute location.
The popup menu may also change if the configuration of an item is changed. For example, if you add feedback to a turnout, the popup menu includes a new item choice called "Tristate". Tristate allows you to use the inconsistent icon, which is one of the four possible icons available for a turnout. Normally when you first click on a turnout icon it commands the layout to change the state of the turnout. If you use feedback for a particular turnout, the icon display will wait to hear from the layout before modifying the turnout icon to the closed or thrown icon. By using Tristate, the icon will change immediately to the inconsistent icon when the turnout is clicked. Inconsistent in this case means that I've commanded the turnout to change and now we're waiting to hear if it actually happened. If and when the layout returns the actual or "known state" of the turnout, the icon will change to that state. If you don't use Tristate, when you click on the icon, it may take some time (milliseconds to seconds depending on the system) before the icon responds with the known state of the turnout.
The marker's popup menu allows you to change the marker's color, font size, style, and color. The menu also allows you to remove the marker from the panel.
If you want to keep your markers between operating sesssions, you can save the panel and the markers will be saved to your panel file.