I caught my daughter (4yr old) touching her private parts under the blanket. I also caught her using the shower hose and spraying it there. I asked her why and she replied it felt good. What is the best way to teach her about this?

Parents often have similar question to yours!!! Children are curious by nature. It's not for sexual arousal but to satisfy their curiosity. This is not something abnormal. Resist initial impulse of getting angry or punishing your child. Just calmly make her understand what's private (e.g. body parts under swim wear) and that touching/exposing private parts are not acceptable in public. Keep your communication channel with her open and discuss openly if she has any questions. After all being a parent is not easy!! She will grow out of it as she gets little older.