Theory:

     He taught the two girls to sing Raga Megh. They practiced night and day for two weeks. Tansen told them, “You must wait till the lamps start burning, and then you start singing.”
 
     The legend goes that on the appointed day the whole town assembled to hear Tansen sing Raga Deepak. When he began to sing, the air became warm. Soon people in the audience were bathed in perspiration. The leaves on the trees dried up and fell to the ground. As the music continued, birds fell dead because of the heat and the water in the rivers began to boil. People cried out in terror as flames shot up out of nowhere and lighted the lamps.
Explanation:
 
As decided, Tansen started training his daughter Saraswati and her friend Rupvati to sing Raga Megh. They were extremely working hard, practising day and night for about two weeks. Also, Tansen had given them instructions in advance to both of them. He asked them to wait untill the lamps start burning while he sings Raga Deepak and then start singing Raga Megh.
 
On the appointed day, people from the whole town gathered near the place where Tansen's Raga Deepak arrangements are made.
 
Tansen started singing Raga Deepak. As he began singing the song, it seemed that the whole moisture in the air got evaporated. The whole town gathered near him, bathed in their sweat. Even leaves from the trees got dried up and fell to the ground. As Tansen continued singing Raga Deepak, birds fell dead. Water in the rivers started to boil. The whole crowd got collapsed for a while. There was a lot of chaos happened around due to this sudden, unfavourable situation. People were filled with fear and threat on looking at the sudden flames which come on their own, that lighted the lamp.
 
Meaning of difficult words:
  
S.No
Words
Meaning
1.
Chaos
A state of total confusion
2.
Perspiration
The process of sweating
3.
Unfavourable
Bad condition or situation 
Reference:
National Council of Educational Research and Training (2006). Tansen (pp. 15-19). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.