I'm in courts quite frequently (mostly as a spectator)... it's really not bad. If anything it's rather boring to a layperson (of course to me, it's the most exciting place ever).
From the sounds of things, you're a witness not a defendant, right?
As a witness you don't really have a lot to worry about. Just answer the questions that the attorneys ask to the best of your ability. If you don't understand a question, don't be afraid to say so.
You're only 14, so the attorneys are going to treat you with kid gloves. The other side might ask if you've ever been convicted of anything, but he won't treat you as a hostile witness unless you give the judge a reason to let him.
Just answer what's asked and don't be a smartass. You'll do fine. No one expects your recollection to be perfect, they just expect you to do your best and tell the truth.
It might be a little boring, but it might also make you feel better... so I'll give a brief summary of what actually happens in court.
1) (if it's a jury trial) Voir Dire: This is the first stage of the proceedings. It's where the attorneys pick the jury members. They'll ask the prospective jurors questions and dismiss those the ones they don't want on the jury.
2) Opening Statements: The attorneys will give their opening statements. They can get long, but they average at around five minutes for each side.
3) State's Case: The prosecution will call their witnesses. Each witness will be sworn in by the bailiff when they're called. The prosecutor will ask questions of them, usually in a friendly manner. This is called "direct examination" (usually just "direct"). Once the prosecutor finishes asking questions, the defense attorney has to opportunity to question the witness. This is called "cross examination" (usually just "cross"). Typically the questioning during cross is not as friendly as that of direct, but it does not degenerate into the screaming matches you see on TV. After cross, the prosecutor has an opportunity to question the witness again in what is called "re-direct." Likewise, after re-direct, the defense attorney as another opportunity to question the witness in what is called re-cross. This cycle continues until both attorneys have no more questions for the witness. This process of questioning repeats itself for each witness that the prosecution calls.
4) Prosecution Rests: Once the prosecution finishes calling witnesses, it will rest its case. At this point, the defense attorney will move that all charges be dismissed on the grounds that the prosecution has failed to make a prima facie case against the defendant. The judge will deny this motion (they almost always do, its simply a motion that all defense attorneys make at this stage regardless of whether it's supportable).
5) Defense's Case: This works exactly like the state's case, except it's the defense attorney calling witnesses for direct, and the prosecution cross examining them.
6) Defense Rests: The defense will rest once it finishes calling witnesses. At this point the defense attorney will likely renew his motion that the case be dismissed. Again, the judge will likely deny it. Especially if it's a jury trial.
7) Closing Arguments: Each side will give their closing argument. Don't worry about the procedure of who gets to talk first and last... it doesn't really matter.
8) Jury Verdict Reading: The jury will now go their little room to discuss the case amongst themselves and come to a unanimous decision. When they return, the foreperson will read the verdict to the judge and the defendant.
More happens from here, but you likely will not have to worry about it. If you're just a witness, your role in the trial is essentially over.
EDIT: Civil trials can be a bit different in terms of procedure. A simple tort case will be very similar to what I described above. A divorce or other family law proceeding could be considerably different.
