When you request a hearing, the magisterial district judge will send notices to you and the police of the date and time of the hearing. You have the right to be represented by your own lawyer at the hearing, but you do not usually have the right to be represented by a public defender or a lawyer appointed at public expense if your conviction will only result in a fine.
At the hearing, the police officer and other witnesses for the prosecution will testify, then you or your attorney may ask questions of the police or others who testify against you. You can then produce your own witnesses and testify yourself if you wish to do so. The police or district attorney can question you or any of your witnesses. The police can then introduce any additional evidence to contradict or disprove what you or your witnesses said. Finally, each side is given the opportunity to make any concluding statements or arguments to the magisterial district judge.
The magisterial district judge will then decide the case. If you are found not guilty, all security you posted will be returned to you. If you are found guilty, the security will go toward paying the amount of the fine and costs.