Creating a card independently of creating a Wrap is useful for a number of reasons. You may want to do this when you are designing a template card that will be localized depending on the Wrap it will be used in, or when you are creating cards that will be placed in a Wrap by an API based on certain conditions.
From the Cards Tab, click on the "Create New Card" button:
This will launch a modal. Pick from different Card categories on the left. Options include your existing Cards or Wraps (My Cards; My Wraps) as well as a whole set of Card Types and Templates to choose from. The right side of the modal will reflect the selection made on the left side and will display Card templates along with a range of card layouts for each template. Select the template/layout combo that you like and click the Create button at the bottom to create a new card.
Before your new card appears in your Cards Tab, you will be taken into the Card Edit screen which will allow you to name the card, add tags, and make any initial content changes you might want to make. (Note: you are required to make at least one change before saving. If you just want to get the card saved and edit it later, just give the card a name and hit Save.)
Once you're satisfied with your changes, click Save. This will save the updated version of the Card to your Cards Tab (in same Collection that you started the Create Card flow from.) If you have no more changes to make, select Close to exit the Card Editor, and notice the new card at the top of your current Collection.