1) On the galleries page, click the edit gallery button for the gallery you wish to find the URL for, Click the Preview gallery button, then select the gallery type. This will open a new window with the gallery in it, copy the URL in the address bar to use in your links.
2) To assign the gallery to a product, either add a new product or edit an existing product, on the description tab, go to the Long description, in the HTML Editor Toolbar, click the last icon on the right of the bottom row, next to the anchor icon to insert a gallery.