You also have the choice to comment on an item on it's page. Though, when in Portal 2, at the end of a test, you are asked for a rating for the Steam workshop, without actually going to the page.
When at a page for a Steam workshop item, you can rate it: thumbs up or down. For example: if I subscribed to 'Portal 2 map name' every time I loaded Portal 2 (assuming that's what it's used for) it would be at the latest version, ready to play. Using it makes it so you will be kept up-to-date with whatever you downloaded. When in a workshop that allows you to download content, it will have a 'subscribe' button.
