When you choose the scribble icon in the tools menu, you will see a Road Snap option pop up just under the toolbar.
Click the checkmark so it appears blue and then you will be notified of how many levels you must zoom in or out to use the Road Snap option.
Draw your desired line and it will snap to roads and paths which are visible. Careful that you are not drawing over too many choices of road
as you will get more lines drawn than you may wish.
Once you have the line drawn that you wish, you may zoom back in or out, place markers along the path, change the view or move sections of the line.
To change portions of the line or route, choose the pointer tool and hover above the section of line.
Click down on once of the squares and holding down, drag the square to the desired location.
(Here you will see that Open Street Maps OSM was chosen as a style)