Updated: Mar 2, 2020
Markers are an essential tool in the Premiere Pro CC toolbox, yet somehow not many editors tend to utilize them.
Generally, there are 3 types of markers that are available: comment markers, segmentation markers and, web link markers.
Comment markers are used to make notes on specific points on the timeline.
Segmentation markers can be used to apply notes to the entire segment on a timeline.
A web link marker can help you attach a URL. Web link markers can also be exported and video players that are compatible with it will generally launch a link to the attached URL.
The shortcut to apply a marker on the timeline is hitting the 'M' key. It appears as a little tab on the timeline. This is essentially the same concept as applying sticky notes to your books. Hit 'M' once more and it will launch the marker window which will allow you to add comments and also change the color of the respective marker. This is the window that will allow you to make the marker into a segmentation marker and also allow you to apply a URL to make it a web link marker.
People that use markers; generally apply different colors to different kinds of markers. This allows them to color orient their project and makes it easier for them to remember what changes need to be applied to a specific colored marker.
To sort out all the markers in one place; go to Window > Markers. Here you will now be able to see all the various markers by color and you will be allowed to read all of your notes. If you double-click on a marker, it will jump to the respected clip or sequence in the project.
This makes things a lot easier while editing a larger project which goes through a number of approvals.