To merge elements in the Main Menu select Model -> Merge.
Arguments:
The dialogue box to merge 2 quadrangles is:
Merge 2 Quadrangles
Arguments:
The dialogue box to merge 2 edges is:
Merge 2 Edges
Arguments: 2 vertices (v1 and v2)
The dialogue box to merge 2 vertices is:
Merge 2 Vertices
TUI command: Merge elements