To add a track Piece
There are three methods for adding new track:
Method 1: Click

Method 2: Drag and drop

Method 3: Shift-click to connect to the most recently added component

TIP: To undo the most recent action, click the Undo button, or press Ctrl Z.

Page url: http://www.anyrail.com/help_en/index.html?addingtrack.htm