Guardians ad litem tell the court what is best for the child in things like custody and visitation. They do an independent investigation. They do not work for court services or child protection.
They talk to the child, the parents and other care-givers. They can talk in private to counselors, teachers, family members and friends, and court services and child protection workers.
They write a report to the court saying what they think the judge should order. The judge does not have to do what the guardian says but takes the report very seriously.
It is important for you to cooperate with the guardian ad litem. Their report can help or hurt your case. Remember: thinking about what is best for your child should be your top priority.