There are various objects which are placed on different tracks where they can be edited. The track head shows you which object type the track is suited for. See Editing objects.
Audio tracks and Sound object properties
Picture tracks and Picture object properties
Picture tracks and Text Object Properties
Video tracks and Video object properties
Universal tracks and Notes object properties
Universal tracks and Data object properties (available from the Advanced License and up)
Universal tracks and Switch object properties (available from the Advanced License and up)
Marker tracks and Marker properties (available with a Starter license and up), Value marker, Command marker (available from the Advanced License and up)
See also