What it means
Prima facie means "on the face of it" or "at first sight". A prima facie case is one where the evidence presented is enough to support a finding in your favour unless it is contradicted or rebutted by the other side. In Australian courts, establishing a prima facie case is often the first hurdle: if you can't show one, the matter may be dismissed early. It does not mean you have won — only that there is enough to require an answer.
How it's used
The unpaid invoices and signed contract established a prima facie case that the builder owed the money.