Select the region you wish to copy, and type //copy, of course. I usually stand in the center of the selection so that it pastes with me in the center. Do //paste to paste. It takes a bit of practice to perfect, but you eventually get the hang of it. I've for the most part mastered it, but even I make mistakes occasionally. But as said, I suggest standing in the exact middle to do it right, because if you're standing up in the air to copy it, and paste it on the ground, it'll end up in the ground.

Move command moves the selection not blocks itself

I haven't used worldedit for a year or two now, but isn't there a "//move" command? Just select the area with the wand, and then use "//move [block distance] [direction]"
For example, if you want it to move 5 blocks forward, and you're facing north, the command would be "//move 5 n"
(To find the direction you're facing, look at the clouds. They always move north)

Okay here is the main key to it...

Firstly do //wand, and right click and left click respectively to select the same as a 3D box. Then, say you were copying a house, stand at the door of the house ground level, if you were about to enter the house, and do /compass (must have essentials installed) and the compass will show u a direction eg North. Now go to your new location, and face the direction north, keep facing directions until /compass shows north, and now, standing at ground level do //paste. Use //paste -a if you are just pasting in air or flat land, it will save you CPU and RAM usage. And thats pretty much the key idea behind it.

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It pastes relative to the block you copied it from. If you were standing at the front door of a house when you copied, then you would stand where you want the front door to be when you paste. If that makes sense

ik but some people paste stuff in the perfect spots in the 1st try

Select it with the tool? Either that or go to the spot and let it paste next to you on that spot.