The first stage of litigation involves an exchange of written documents (pleadings) in order to define the nature and extent of the dispute.
The plaintiff sends a statement of claim to the defendant, setting out the basis and the extent of what is being claimed.
The defendant replies with a written plea, indicating their intention to defend the claim and setting out what matters they dispute.
Further documents might be exchanged until the exact issues between the parties have been sufficiently clarified. The case is then ready to go to trial.