Segment Actions are available when one or more segments which belong to the same path are selected:
These functions are only enabled when Segment Selection Mode is on. To set up Segment Selection Mode, check "Tools / User Options / Geometry Editor / Segment Selection Mode". After enabling it, individual path segments get highlighted when you click on them as long as they belong to the same path. Hold Shift key and left click on segments to select more segments of the same path.