Multi component selection lets you select faces, vertices and edges without having to change between selection modes. In this mode, you select components based on the mouse cursor’s proximity to them.
To turn on multi-component selection mode for all objects, press the Select by component type button on the status line and then -click the Select miscellaneous components button and select Mesh Multi Components from the menu.
If multiple components of different types are already selected, then Maya selects components based on a hierarchy of vertices, edges, and then faces. For example, if an edge and a face are already selected and you perform a marquee select on the object, Maya will select all edges in the marquee.