My teenage daughter has reached the age of puberty. How do I explain her about the menstrual cycles?

It is always best to share the right information with her at the right time, so that she can be prepared for the day when she gets her first period. As debolina mentioned, i would also say prepare a sanitary kit and keep for her. you can start talking about it to her while you both are watching TV and the ad pops up, or when you are in the store and see sanitary napkins. just ask her casually if she knows what they are. you may be surprised to know that she already knows about periods. a friend of mine broached the subject with her 10 year old who was already aware of everything, as they had been taught in school. so bring it up, keep the conversation normal and also tell her about your own experiences.