how i can find the "center mass" point in a  aeria???

See the related tips below your question (generally: with MASSPROP).

you need to create region of your area. Than select region/massproperties command and select you object. You'll have listed all the properties like centroid, moment of inertia and so on. Do not forget that everything is related to the chosen 0,0 point (axes), so if you want to have correct props, you need to change 0,0 point into the center of your object.

See also the CENTROID utility (Download) which will actually draw the "center mass" point.

I downloaded the VLX file. How do I activate the command?
 

Just use APPLOAD to load the VLX file and run the CENTROID command.