Select the first End-Point, drag away to specify the angle of the curve at the first End-Point and then release. Next select the second End-Point and drag it to position. When you release, a curved track segment will be created between the two End-Points.
A straight track will be created if the second End-Point is lined up with the first End-Point.
If the Snap Grid is enabled then the End-Points will be constrained to the grid.