Hey buddy, via profile stalking I heard about you wandering about how to make 3D text in GIMP.
best way I figured out is to go to create layer>create logo>alien glow. Select the font you want, and set the glow color as black. When its created, delete the background layer. Duplicate the shadow layer to the intensity of your liking. You can also move the shadow up or down to give it a shadow from a specific point.