A URL is sort of like an address to a web page. For example the URL for your question is: http://answers.microsoft.com/en-us/windows/forum/windows\_7-performance/how-to-cut-paste-a-url-into-my-browser-what-is-url/2731cc73-6177-4b5f-964e-8733d5f023d6
If you look near the top of your web browser (e.g., Internet Explorer) you should see something like that (only part of it may be visible for space reasons). Here is some more info re URL: http://en.wikipedia.org/wiki/Uniform_resource_locator
To cut and paste a URL you normally just need to drag your mouse over it so it is highlighted then press Ctrl+C to copy and then move to where you want to paste and press Ctrl+V to paste.
If the URL is a different color and underlined like the one I have above to the wikipedia site, all you need to do is click on it go go to that site.