Creating cards from webpages
You can quickly create new cards for web pages by dragging the URL of the webpage onto 'Add a card..' within a list. You can also copy and paste the link instead.
While on the website, click the URL in the browser address bar and then drag the URL onto the window with the Trello board. There, let the link drop over 'Add a card..' in one of the lists. Alternatively, copy and paste the link onto 'Add a card..'.
This will automatically generate a new Trello card with information that can be gathered from the website. Depending on the content that the website provides, you'll see a card cover picture and a description of the website. The URL to the site is automatically added as an attachment to the card.
Using the 'Add Card' bookmarklet
Setting up a bookmarklet will also let you quickly convert a link to a card. Here's how to get that set up https://trello.com/add-card