There are two kind of markers: timeline and clip. They are like sticky notes for the timeline or clips. There are three ways to show or hide a marker track:
Click the down arrow on the top/left of the timeline and then select Marker
Select View > Show Marker Track from the menu
Press CTRL + M on the keyboard
If you used markers, you MUST save the content with the SmartPlayer.
To add a marker, move the cursor to the small black bar at the bottom of the timeline bar or top of a clip and wait for a blue diamond and plus sign to appear and then click.
Right-click and select Rename to open the properties panel where you can then add a descriptive name for the marker.
Press CTRL + ] or CTRL + [ to navigate to the next or previous marker. Add the SHIFT key to make a selection between two markers.
You can press SHIFT + M to add a marker even if the marker track is not opened.