Hot keys

The usual hot keys work in the editor:

Shift + arrow for select
Ctrl + C for copy
Ctrl + X for cut
Ctrl + V for insert
Ctrl + Z for undo
Ctrl + Y for repeat

Mouse

Of course you can also select with the mouse and use your browser's editing features.

Linux / X11: A left doubleclick selects and copies a word, and a click on the middle mouse key is insert.