The key bindings of Emacs predate modern GUIs, and the keys that were
chosen by later GUIs for cut and copy were given important functions
as extended keymaps in Emacs. CUA mode attempts to let both bindings
co-exist by defining C-x and C-c as kill-region and
copy-region-as-kill when the region is active, and letting
them have their normal Emacs bindings when the region is not active.
Many people find this to be an acceptable compromise. CUA mode also
defines a number of other keys (C-v, Shift selection), and can be turned
on from the Options menu.