Yes, I give evidence in Court in a professional capacity as expert witness.
Courts can be intimidating places, but most have a witness care unit that should guide you through the process. Are you sure it's a Crown Court? CC is usually for criminal cases -- other cases are usually held in county court, magistrate's court or family court.
It helps if you can get to see the inside of the court before you are called to give evidence, so you know what to expect. In a Crown Court the witness will stand in the witness box (an usher will lead you there, and provide you with drinks of water if you need them). To one side of the witness box is the judge's bench which is raised up. The jury (again, Crown Court) is usually opposite the witness box, while the dock (where the accused stands) will be somewhere opposite. There will be benches in the middle for barristers and solicitors, and a set of benches to one side for press and public. The exact layout varies, but those are the main features.
The trick when giving evidence is to take your time. Compose an honest answer in response to the question, give your answer and then stop. If you can't answer a question, then say so. Don't be led into wittering on nervously just to fill the silence. Sometimes the other side's barrister will ask the same question repeatedly in the hope that you will change your story; if you're confident of your answer, just give it calmly for as many times as they ask. Barristers love asking: "But is it not possible that x happened?" while outlining the complete opposite of what you've just told them. All manner of things are possible, so don't be drawn into speculation. If you think y happened, then just keep saying so.
On the whole the courts go out of their way to be polite to witnesses -- it bears v. little relation to high legal drama on telly, just as real police station interviews bear little relation to DI Frost & co. The other side's barrister has a duty to test your evidence, so it's reasonable to expect some searching questions, but this shouldn't degenerate into bullying.