Which method are you attempting to use?
The way that I'd do it would be this:
1. Select the relevant text. (Drag the mouse cursor across it or, if it's a paragraph, triple-click on it. If it's a URL in the address bar, simply right-click on it)
2. Right-click on the selected text. (Not required if it's a URL, 'cos it's already been done). Select 'Copy'.
3. Go to the location where the text is to be pasted, right-click and select 'Paste'.
If that doesn't work for you, where is it going wrong?