do you know??Is it necessary or not ??

Hello everyone
I need your help
I just want to know if it's necessary to write an introduction for each lesson
or not ?because I'm a student teacher and when I have explained a grammar lesson
about ''articles'' without introduction the teacher there told me that
a perfect lesson should contains"
pre-presentaion
presentation
post-presentation
what do you think?
and if I have to do so what kind of introduction would this be?
because she gave me a chance to write my lesson plan again

i don't know

you can use a song for any grammatical rule
or a game