The Grab Vertex function is used to pick up and move all coincident line segment end-points and vias at a an interior point of a multi-line track.
To grab a vertex, you must first position the cursor on or very nearly on the desired vertex and then press <left mouse> or <Enter>. The cursor will jump to the precise vertex point.
When working in a densely populated area, it is useful to pre-select the desired target layer.
Vertices of lines contained within components are accessible only from the proper layer.