Cheryl has been accused of something called "racially aggravated assault" and another charge of hurting toilet attendant Sophie Amogbokpa.
She denies the charges.
The trial opened on Thursday at Kingston Crown Court in Surrey. It is expected to last up to five days.
If Cheryl is found guilty by the court jury, she could go to prison.
Cheryl was in court for the first day of the trial, but she wasn't giving evidence.
Sophie told the court her version of what happened.
She claimed that Cheryl got violent when she asked her to pay for some sweets which she was selling in the toilet.
"No other girl had ever behaved that violently in the toilet before," said Sophie.
Cheryl's lawyer denied that the singer had made racist comments.
He pointed out that Sophie had even signed a police statement which made no reference to Cheryl being racist.
He also suggested that Sophie started the fight.
The case continues.