The Add Menu has all the actions related to adding track pieces to the layout.

Straight Track Ctrl+G - lay straight track pieces of arbitrary lengths
Curve Track - lay curved track pieces using different modes for selecting start and endpoints and radius (Curved Track).

Circle Track - place a circle of track by selecting radius, tangent and or center (Circle Track).

Parallel - create parallel track or line to existing flex-track, straight or curved track. (Parallel Track or Line)

Fixed-track Ctrl+T - select a piece of Fixed-track and place on layout.
Hand-laid Turnout Ctrl+Shift+I - lay a turnout in place on the layout. (Hand-laid Turnouts)
Structure Ctrl+Shift+C - Add a predefined structure to the layout.
Helix Ctrl+Shift+H - Add a helix. (Helix Track)
Custom Turntable Ctrl+Shift+N - Place a turntable. (Turntables)
Control Element - Create a control element.
Block - Create a block. (Block)
Switchmotor - Create a switchmotor. (Switchmotor)
Signal - Create a signal. (Signal)
Control - Create a control. (Control)
Sensor - Create a sensor. (Sensor)
Straight Track
Structure
Fixed-track