Copying and pasting is something you'll do a lot of with HTML, here's how to do it...

Place your mouse cursor (the little arrow thingy you move about on your screen) at the beginning of the area you wish to copy. Hold down the left-click button and slide the cursor of the area so that the text becomes highlighted.

Then place your mouse cursor in the highlighted area and right-click and click on copy.

Now place your mouse cursor at the place where you wish to paste the text you copied and right-click and click on paste.