What program are you using? If entry and deletion are possible in a given
window, then if you select some text, then Cut (and Copy) would be availabe.
Once text has been cut or copied to the clipboard, the Paste would be
available, assuming that inserting text into the current window is allowed.
Hence, Cut and Paste would work in Word.
However, in an Internet Explorer window, if you select the displayed text,
Copy is available, but Cut and Paste would both be grayed out because
they're not valid options. In a text fill-in space, however, both (as well
as Copy) should be available when text is selected.
I hope this helps.