Cards

You can create any number of cards to any column. 

Cards Creation:

click on the add card button, fill it out (this is a ck editor instance, it supports rich text and IPS features such as @mention).  There is no limit to how much text can be written here, but keep in mind its meant to be a "title" area for the card. To save a card, just click outside of the card and it will auto save.

Assigning Cards:

You can assign a card to up to 10 people (default is 6, but you can change this in project settings). You can also claim the card for yourself. 

Card Moving:

you can move cards vertically in a column to reorder them, or drag and drop them to another column. 

Card View:

if you click on a card, it will open up in a popup, giving you access to various things. you can add a description for the card, add a list, mark a card complete, set a due date, view the history of a card and/or add/read comments.

Archiving Cards:

there is no way to "delete" a card, but you can archive it. grab ahold of a card and drag it to above where the columns display, the archive area will open up, allowing you to drop the card there. you can retrieve a archived card at any time.