following+howto

follow a card

Whenever you are logged in, the card menu will include a top-level "follow" link.  Click that link to follow that card.

follow all cards of a given type

Navigate to a Cardtype card, and then follow the same procedure as above.

unfollow a card

If you are following a card, the menu link will read "following" instead of "follow".  When you mouse over it, it changes to "unfollow".  Click that link to unfollow the card or cards.

see what cards a user is following

There is not yet quick interface for this, but you can go to |user's card|+*following to see a pointer card that indicates which cards a given user is following.   When a signed-in user clicks "follow" or "unfollow" anywhere on the site, this card is automatically updated.  It can also be edited directly like any pointer.