The basics of forge mode are;

Turning into a monitor using up on the D-pad.

Spawning Objects with X, scroll through other stuff with the bumpers and spawn with the A button.

Deleting the object that you don't need using Y when the ridicule turns green.

Carry The object by tapping A once when looking at the object.

To make any objects float you must first make a base for them (like a stand)and build on top of that until you can see where you have to stop.(Some maps have more height than others)
Then when you have what you want on top of the other object(s) delete the other stuff under it and it should be floating now.

Enjoy :)