Subscriptions allow you to watch for bookmarks that contain important tags. Once you have added a tag to a subscription, Delicious will watch all public bookmarks saved with that tag and deliver new ones to your subscriptions page.
To add a tag to your subscriptions page, click on the drop-down arrow next to tags and select My Subscriptions. To the far right click on Add a Subscription; this will open a new box on the right that will allow you to enter a specific tag. Once you have entered the tag click the add button; this will populate the subscriptions page with bookmarks that include that tag. You can edit or delete subscriptions by selecting Subscription options on the upper right of the page.