Through (TOOLBOX-LANDSCAPE-TERRAIN-MANUAL-BRUSHES) you can find the road tool. Click on it once to enter drawing mode then start drawing the points making up your road. You can click and drag to make the road curve and then double click to end road drawing.
With the road points drawn, you can click on of them and then show the details panel. Now you can change the ground material or increase the width to make the road wider.
