If you are working in wireframe view, you can hold the intelligent cursor over the edges to discover which ones can be used to create a chamfer. If an edge or a path is highlighted, you can use it.
If one of Follow Continuous Edges, Chamfer a Face or Chamfer Away From A Face is selected and you hold the cursor over a valid edge, a path may highlight. Otherwise, the single edge highlights. Full details on these options are given below.
You can select, append, or deselect edges to an existing path as follows:
The selected edge is highlighted. This is the first edge in the path.
Press and hold the Shift key and click to add a track to the current selection.
Press and hold the Ctrl key and click to add/remove tracks from the current selection. You can also use Ctrl+click to join separate tracks into a single track and to split a single track into two separate tracks.
Select the Follow Continuous Edges option and use Shift+click or Ctrl+click on a selected path, to deselect it.
In the example, deselect the Follow Continuous Edges option and select an edge at the end of the path using Shift+click.
The edge is now highlighted as part of the path.
Now Ctrl+click the edge again.
This removes the edge from the path and we are left with the following.