Some courts may use God in their courtrooms while other courts may not.
I've personally never had to say so help me god in court and if you do have to say so help me god and don't believe in god then they cannot legally force you to say so help me god.
When you go to court you'll be asked to raise your hand and swear to tell the truth the whole truth and nothing but the truth.
If you refuse to swear to tell the truth or raise your hand and swear to tell the truth then you could be held in contempt of court which could mean you might serve some jail time which is usually 30 days.
The best thing to do in court is to follow the judges directions and raise your hand and swear to tell the truth and you must tell the truth or you could be in jail for lying in court.
I never had to swear on a bible but only had to raise my hand and swore to tell the truth and I had no problem doing so because I had no reason to lie about anything in court.