What are you trying to make in 3D? A logo? An object? How versed are you in Inkscape?
The tutorials listed above are the best way to get started. Personally, I've gone through a few HeathenX tutorials, myself, and found them to be just the best.
Start simple and work your way through. Take one small object at a time, and shape it to your liking, and move forward that way. There are many simple ways to make stuff look 3D, such as the logo for the new PCLinuxOS wallpaper I just posted. Doing something more complex, such as Gemini's robot, will take more time and patience.
The one below is nothing more than a few layer tricks. I started with a logo and made the lettering black, duplicated it, made it gray, moved it up a few notches with the toobar arrows to just hint at it having dimension by giving the edge a highlight, and put that layer below the first. I then duplicated the logo again, blurred it, offset it downward by pressing the down arrow twice, and put it on the bottom. Next, I duplicated the logo, again, and made it a white to transparent gradient and then cut some off by creating a rectangle and placing it where I wanted and chose Path->Difference, then aligned the gradient with the gradient path tool. I repeated similar steps to make the red, but the final whit part goes on the top most layer over it all, and the gray on the "Ridiculously simple." part. Voila...a 3D effect on the PCLinuxOS logo. See how simple that is? It stands off the page really nice.
I just want to make a simple 3d wallpaper of a simple object like a phrase or image etc. Just something to wet my feet so to speak. It will be my first one. I need some info just to get me started. The provided links should help.