Put the mouse at the beginning of what you want to copy and click the left mouse button, holding it down while you drag over the section.
Drag across or down. At the end of what you want copied, let go of the mouse button.
What you want to copy should be highlighted!
(If you make a mistake, click the mouse button once to unhighlight, then start over.)
While it's highlighted, hold down the Ctrl key and hit the letter "c". This copies the highlighted part to an invisible clipboard.
Now go to where you want to paste it. Put the cursor on that spot by clicking the left mouse button once. Now hold down the Ctrl key and hit the letter "v" to paste what you copied.