Sharmi you may write these points for your essay..
what is ponggal
when is ponggal
regional significance
history of ponggal
legends of ponggal
traditions and customs
meaning and significance
ponggal preparation
4 days of ponggal
ponggal date

you can also strart with a poem:
pot rice to Sun God
sugarcane to cow and ox
sweet rice for you and me
good milk to friends and family