Order as to costs: explanation needed

I'm helping a fellow layman who was the claimant in a county court case. The defendant won the case and was ordered costs. The order states

"The Claimant to pay the Defendant's costs to be assessed in default of agreement not to be enoforced without order of the Court".

What does this mean, exactly? As an order for costs has been made, what's the purpose of a further order?

Thanks.