I recently found the keyboard shortcut so that, after having selected vertices, you could press it, and it would automatically join triangles that should obviously be quads, i.e the stuff that happens if you subdivide to edges in sequence…
Alt+J converts triangles to quads but you can also select two adjaceent tris and press F to change them to a quad.
In the 3d view just look in the Mesh menu and then Faces / Edges / Vertices for many functions and their keyboard shortcuts.