The easiest way to copy text is by drag and drop: select the text you want to copy (see Selecting text), place the mouse over the selection, left-click as you depress the Ctrl key on the keyboard, and drag the text to a new location.
Alternatively, select the text, right-click and then select Copy from the displayed menu (or click on the Copy button on the toolbar). The text stays where it is and a copy is put into the clipboard.
To put a copy of the text into the document (or into another document), click where you want the copy to go (the cursor indicates where the text is to start). Right-click and select Paste (or click the Paste button on the toolbar). The text will be "pasted" into the document.
See also: