Although courts do deal with long lists, trials are listed separately. The trial in which you are involved may be “double booked” with another. The court usually double books as a large number of trials do not proceed for various reasons. If both trials are ready to go the court will have to decide if they can accommodate both or if one has to be adjourned to another day, so be prepared for that.
Every court has a Witness Support service:
http://www.victimsupp...rg/Help-for-witnesses
They will be there to see you through the trial day, but if you contact them earlier they can arrange for you to visit the court beforehand.
You will be kept in a separate waiting room to the defendant, though the layout of some courts makes it impossible to ensure that witnesses and defendants can be kept apart entirely. Tell the Witness Support service of any concerns you may have and they will help you.
If you do have to give evidence it will be on oath (or affirmation if you prefer). The prosecutor will ask you questions about the events you witnessed. These will be based around the statement you gave to the police (which you will be able to see beforehand to refresh your memory). You wll probably be cross-examined by the defendant's advocate (and be prepared to have your version of events challenged). Finally, be prepared for delays and possible adjournments.