Magistrates will be given any advice on the law they need from the legal adviser. Legal advisers sit next to the magistrates and advise them on points of law to help them come to a decision.

The burden and standard of proof 

In a criminal trial the burden is on the prosecution to prove that an offence took place, not on the defendant to prove that it did not. This is called the burden of proof.
The magistrates or district judge have to be sure that the defendant is guilty before they can convict him. If they are not sure they must acquit him. This is called the standard of proof. It is the prosecution’s responsibility to present enough evidence so that the magistrates are sure.
If a defendant is found not guilty, it does not necessarily mean that the magistrates/district judge did not believe the victim, it means that there was insufficient evidence for them to be sure that the defendant was guilty of the offence that he was charged with.