You will add a curve that is tangent to the last segment you added to the sketch. The curve will form the corner of the road casing. Ctrl-T is the shortcut for creating segments that are tangent curves.

The Z, X, and C keys are shortcuts that let you Zoom in, Zoom out, and Pan while editing.

When you create a tangent curve, you must specify two parameters for the curve from the following options: arc length, chord, radius, or delta angle. You must also specify whether you want to create the curve to the right of the line or to the left of the line, according to the direction in which the line was drawn. The curve is created from the last vertex of the existing segment based on the parameters you defined.