When you first arrive at court, you will need to go through security, this applies to everyone who enters a court or tribunal building. Please see the link in Related Information for items you are not allowed to take in.
Once you have passed through security the best thing to do is to find the Witness Service desk or office. They have a list of all witnesses due at court on that day. They will be able to tell you which courtroom to attend, where the canteen is and where you might find the officer in the case. The reception at the court will also be able to tell you where to find details of the courtroom.
For more information please see the websites in Related Information.