GDI object (is a graphical device object) used to write on a
device context for graphical output. 
GDI objects are: Pen, Brush, Font,Line, Rectangle etc.
These objects are created using their corresponding win32
function. For eg, CreatePen, CreatePenIndirect are used to
create a pen object.
After these objects are created they would need to be
selected to the device context before processing using
"SelectObject" function. 
GDI objects are not associated with any device context
during its creation. SelectObject function does that
assocaition.
Once an object is selected into the device context it would
be available until the object is destroyed through
DeleteObject or the program exits.

GDI(Graphical Device Interface)having the collection of 
Objects(pen,brush,cusror,bitmap..) thats are Interface to 
the Graphics. To handle Grahics Objects we are using the 
HDC (Handle Device Context)In Win32 API.for selecting the 
object we r using the SelectObject(HDC,Object) function. 
and after compleetion For Releasing Object we r  using 
ReleaseObject(HWND,HDC).