Specify whether you want certain NURBS modeling commands to behave like actions or tools. An action performs a discrete function on selected objects. A tool lets you manipulate objects until you complete the operation. You may want to change actions to tools as you become proficient at Maya’s NURBS modeling.
To globally change the applicable modeling tools, select Everything is a Tool or Everything is an Action. To individually set each command, select Mixed.
Turn on Convert component selection to have Maya automatically convert an object selection to the appropriate component selection mode if an action works only on components.
For example, if you select a polygonal object and try to extrude faces, Maya automatically selects all the faces on the object and proceed.
You have the following options.