First, you would need to create the HUD's image in your paint program, and export it with the right settings.
I'm not sure about GIMP, but
Paint.NET offers different options for DDS files...
A8R8G8B8
See attached image...
Then, you create the HUD in your FPI script as explained in the FPSC Manual, and The Official Guide to FPSCreator.
They are often seen in state=0 because you only need to create the HUD once in the script, and not every time you display it in any other state.
The hud would be created like so...
:state=0:hudreset,hudx=50,hudy=60,hudimagefine=gamecore\huds\
yoursubfolder\
yourimage.dds,hudname=
yourhudname,hudhide=1,hudmake=display
Of course, the names in bold would be unique names that you create.
Then, to display your HUD you would use FPI action...
hudshow=yourhudname
...and to erase it you would use FPI actions...
hudunshow=yourhudname
...or...
hudfadeout=yourhudname
