Most (but not all) Decko sites choose to display a recent link prominently in their navigation.  Even if not, you can usually reach a recent changes page by going to /*recent or /:recent.

If a card was created, the change listing will note that it was "added". If the content of a card was changed, it will note how long ago it was "last edited" (and clicking on those words will show you the change). If something else was changed about a card (eg. its type) it will note that it was "updated".