Selecting Text Without the Mouse

To select text, just add the Shift key to the navigation shortcuts:
Press Shift + Left or Right Arrow keys to select a character at a time.
Press Shift + Up or Down Arrow keys to select a line at a time.
Press Shift + Control + Left or Right Arrow keys to select a word at a time.
Press Shift + Control +  Up or Down Arrow keys to select a paragraph at a time.
Etc.
And to select all the text, press Control + A.
Once you have selected text, you can copy it, move it, format it, etc.
To unselect, simply press an Arrow key on its own.