You give an approval whenever something is acceptable and good. "The school approved the new course material because it focused on learning." Affirmation is given as emotional support. "He nodded in affirmation towards Carol's new idea." In my opinion, affirmation and approval can be interchangeable. However, affirmation usually carries more weight and is formal. A statement is simply a declaration of facts or opinions and can either be positive or negative. "The witness gave his statement to the police."