Hello i installed ubuntu desktop 15.10 in a laptop, but when drag files from all folder, downloads etc... to desktop, the files was copied instead of draged.

Any ideas?

do you mean you wanted to move those files? try to press shift and/or ctrl and/or alt during drag.

also be aware
the "desktop" is more of a decorative thing than a normal folder

normally one places the *.desktop" program launchers in there

you really need to get away from that Window mentality. just saying It's GNU/Linux not Windows ----

dear acer2!
that behavior is probably adjustable.
go into your file manager's preferences and look around.
if not, you simply use ctrl+x or right-click => cut, or maybe some sort of ctrl-click.

OT:

i still remember the days when i had all my files on the desktop, because i thought i'd never be able to find them again if i don't see them.

then, they became so many, i had to create subfolders on my desktop.

then i realised that 75% of the files that i thought i really need, i never accessed again after dropping them on my desktop.

then i realised that i could just as well store them somewhere else in my $HOME, and open the file manager when needed.

then i stopped using a desktop manager altogether.

so you're like strickly command line commando dude now?

no.

in gnu/linux, a desktop manager is an application that provides icons on your desktop and usually also paints over the root window.
XFCE, for example, has it as its own application (xfdesktop), but all other DEs i know of, it's just an extension of the file manager.

it doesn't mean i don't use a GUI.

sorry I must have missplace my brain for a momment, misread, was thinknig of a FileManager Not Desktop manager.