Step 1: To create a card, press this icon on the left hand side of your screen and select "New Card".
Step 2: Choose a title for the card, then select the card category e.g. Cast, Crew, Location, Art Dep, Generic etc.
You can create and edit card categories in Project Settings.
Step 3: Choose the Access (ie let everyone in the Project see it or just you (Private Vault)
You can template a card if you like it so every card has the same format. For more info on templates click here.