Reference elements for alignment

  Question

In 2D model when drawing or moving an element, I want to reference the position to an existing element. In 3D sketching this is done by hovering over a part of the existing element (end, centre, etc.) and a dotted line appears to show that the new elements will start on the same X or Y plane. This doesn’t seem to happen when drawing a 2D model. I am sure it is there so how do I turn this on please?