what are the options for a defendant in terms of what they can do if served a claim?
Admit and pay the full amount to the claimant- this ends the claim.
Admit the claim, and pay in installments- the claim ends when the full payment is given.
Dispute the claim, and file a defence setting out why the claim shouldn't be paid in full or part.
File an acknowledgment of service confirming receipt of the claim but asking for more time to file a defense.
If the D fails to respond, then the C can apply for judgment in default meaning that the C wins and the D can be forced to pay the sum claimed.