This particular feature simply does multiple things with minimal input, a real time saver!
Simply select any edge and click "insert" > "sketch" or just "sketch" on the sketch tab of the command manager.
A sketch plane is created automatically, normal to the edge you selected, with the origin coincident to the end of the line nearest to where the edge was selected.
A new sketch has automatically been opened on the new sketch plane and your free to start.
By Jon Weston-Stanley