Most applications that allow text input also let you copy and
paste text using the mouse. In an xterm, hold down the left mouse
button while dragging over some text. The text will remain highlighted
when you release the button. If you now press the middle button in
the xterm, then the text will be copied. You can also
use this method to copy small bits of text from one window to another.
To start an xterm and have an application (for example top)
running in it immediately, use xterm -e top &. Note that when
you start xterm this way, it will terminate when the program
you're running in it does.