When a Polyline, or multiple Polylines are selected the SELECTION - TOOLS menu will be available. The SELECTION - TOOLS menu contains tools that allow you to edit, change styling, annotate, or perform advanced functions on your selected Polyline(s). The menu dynamically adjust the tools available depending on your item selection, with additional tools available for selecting more than 1 Polyline.

Individual Polyline selection

Multiple Polyline selection

Styling group

LineAllows you to change the Polyline(s) color.
ThicknessAllows you to change the Polyline(s) thickness.

Annotate group

NamePolyline(s) Descriptor & Number displayed over the Polyline(s) in the Viewport.
LabelAllows you to change the Polyline(s) Label color.
SizeAllows you to change the Polyline(s) Label size.

Edit group

Edit VertexEnables Edit mode for selected Polyline. Displays the Edit Vertex Mode box where you can select editing options and change X,Y,Z coordinates of the selected Polyline.

Transform group

To TerrainSelected Polyline(s) will be draped to the underlying Elevation terrain by changing their Z value to the same elevation as the Z level of the terrain at their XY location. 
SplitEnables Split mode. Polylines can now be split into separate Polyline items by left-mouse clicking at your desired split location along a selected Polyline.

Result: Polyline
To BoundarySelected polyline(s) will be transformed into a Boundary item. Line segments between the gaps of the Polyline(s) will be automatically filled in to complete the Boundary and original Polyline items will be removed.

Result: Boundary
DensifySelected Polyline(s) will become more complex by adding vertices to them that drape the Polyline(s) to the underlying terrain. Densify has 3 methods of adding vertices, Break Points, Regular & Low-pass. Breakpoints will add vertices by elevation change along the Polyline. Regular will add vertices at a specified distance intervals. Low-pass will add vertices at lowest elevations along the Polyline at specified intervals. All vertices created will always drape onto the underlying Elevation terrain.
Merge PolylinesMerge separates Polyline items into a single Polyline item. The Polylines must have endpoints that overlap on each other in order to merge. (Only available for use when more than 1 line is selected)

Result: Polyline

Create group

Offset LineCreates parallel line(s) to the selected Polyline. The delta Z Offset Method is controlled in the dialog box. Left-mouse click in the Viewport determines the offset distance.

Result: Polyline(s)
Section LinesCreates a set of Polylines along the trajectory of selected Polyline(s) into a unified layer. Polylines created will be spaced perpendicular along the selected Polyline at designated regular intervals. The spacing is controlled by the Along box. The width of the intersecting Polylines is set via the Across box.

Result: Polyline(s)
Extract PointsCreates Point items at every vertex of the selected Polyline(s).

Result: Point(s)