This looks simple but can be tricky sometimes when you use different apps. In general, these steps can be used in Email or some other apps:
Double-tap or touch-and-hold to select a word.Drag the handles to adjust the area if needed, then tap Cut or Copy.
Tap an insert point, and drag the handle to adjust it if needed.
Select Paste (Hint: tab the handle when the 'Paste' button doesn't appear).
Note: When working in a web browser such as Android's Browser, use touch-and-hold to select a word since "double-tap" has been used to enlarge or reduce a webpage.
