Logic gate circuits can be expressed as a circuit diagram, or as a written logic statement.
e.g. Z = ((NOT A) AND (A OR B)) OR (A OR B)
Each exam board will have their own preference on how to express these written statements, but the principles remain the same.
How to create a logic statement from a logic circuit diagram
The video below takes you step by step through the process of turning a logic circuit diagram into a written logic statement.