Right-click in the address bar of the page you want to link to. (That will highlight the URL). Select 'Copy'. Go to where you want your link to appear. Right-click and select 'Paste'. Job done.
On top of page there's an address beginning with http. Click your cursor on it, it will hilite. Press Ctrl C to copy. Ctrl V to paste address wherever.
ayg - a slightly different method if you want the start screen of your Youtube to fill your post: put the link into the window provided ("enter youtube link here") if you don't want your YT link to dominate your post, just paste it into the text and it will appear like any other link.
AYG:
For the purposes of AB's system, you can completely ignore the 'Embed' button on a Youtube page. Simply right-click in your browser's address bar (to highlight the URL of the relevant Youtube page) and select 'Copy'.
On the AB page, right-click where it says 'Enter You Tube Link Here', and select 'Paste.