"I am happy for you" is an expression used to convey genuine joy and congratulations to someone else for their good fortune, success, or positive life event. When you say "I am happy for you" to someone, it means that you feel pleased and delighted about the positive situation they are experiencing.
This expression is commonly used to show support and share in someone's happiness, emphasizing that you genuinely feel good about their happiness and wish them well. It is a way to acknowledge and celebrate the positive developments in their life while expressing your positive feelings towards them.