Hi!!
Some grammar:
https://youtu.be/ZjhOgnROluo
https://learnenglishkids.britishcouncil.org/category/grammar/grammar-there-are
Exercices:
https://agendaweb.org/grammar/there_is_are-exercises.html
https://www.liveworksheets.com/worksheets/en/English_as_a_Second_Language_(ESL)/There_is_-_there_are/There_is_-_there_are_na601gy
https://www.englisch-hilfen.de/en/exercises/various/there_is_there_are.htm
Enjoy!!