I want to use the Spotlight to position an graphic to a specific spot of my geometry.
Once the graphic is in place and position, I want to create a MASK from it.
How can I do that ?
Spotlight is for painting image textures onto objects. Once the object is painted, there are a number of options in the Tool>Masking>Mask by Color menu for converting color to masking.
An alpha can also be assigned to a masking brush along with an appropriate stroke type to allow you to directly place a mask in a certain shape/position.