To copy text using the standard Android capability, long tap the text, and when the text is highlighted you can see on the top bar a button with two cascading rectangles. When tapped, highlighted text will be copied to your clipboard.

You can then simply paste the copied text into a new email, or wherever you need to, by long¬†tapping until you see that “Paste” appears. Click on “Paste” and the text will be pasted.