Yeah there are several tutorials on places like http://www.lbpcentral.com/ , but you pretty much need to play a level with some 3D glitched material already. You can emit into the other layers, but it seem glitchy, avoid letting a free falling 3D item from hitting the water it may act up, always connect them to somthing stationary (the anti-grav sticker at 100% dampening with 100% anity works well). The back layers take up the thin layer on the back so if you have a mving item in the back thin layer it will collide with any back 3D glitched layer. Don't recall if the same gor for the far front, but you sack boy can't hover around the tront layer 3D items (take up the same space as the hover layer). You can move items in the 3D layers, but it is safest if they are hollo materials.
You can search for 3D glitch on level search and find tons of levels that give as gifts.
This is how it works, place the 3D glitched material on the level, release, then select it (just so cursor moves to that background level...you will see it move back to the item), then goto sack, select new material, place in level and it should be in same layer as glitched material.
Every time you expand it out and the contract it to one thin layer it will move forward a layer (or back if it is an iten glitched in the front layer).
To make an item expand 50 or more layers you place a for and background item in the smae area, select them both, then unslect and place new material and it will span more than 3 layers, that is how I made many parts of the spaceship, city, and dead alien planet., the only issue is if the layers go from the front glitched to the back glitched layer you can walk through them (they act like holomaterial).
Unattached fallying 3D material will break if it collides with other layers.
Movers and such will work on 3D items but see above, if they hit something else the break out of existance.
If you like the following levels of mine use the 3D glitch...
The Choice: Act One (First Curve of Mobious) <---(this one has a moving blimp in the background above the city that is using the glitch...it should have 3D items in prize for beating, but can't recall)
Space Vessel 8212: Centuries Adrift <---(Tons of use of 3D, and should have 3D items as rewards for beating...but very long level...worked on it for a very long time)
Space Vessel 8212: Destinations Gone by... <---(Far, far shorter than the first one tons of 3D, but very few instructions and puzzles and ICO esc in the sense you have to figure out where to go and how to get there...should also have 3D rewards at end)
Aircraft Carrier USS O.K. <---(Some 3D and 3D gifts for beating, but 7 missions have to be beaten using all types of vehicles)
Prism <--(-was built using 3D, but ran into issues with thermo so much of it was removed, but I think you get 3D items as gifts for beating, and you can just hit a button to end level I think, should say in instructions when you start level...if so this would be the quickest way to get them from my levels)