Study Websites and Apps which recommend for every board. The respected links are given below:

https://byjus.com/cbse-notes/ : for every CBSE student of 6 to 12 class

https://byjus.com/icse/ : for every ICSE student of 1-10 class

https://byjus.com/ncert-notes/ : NCERT notes

https://www.savemyexams.co.uk/igcse/ : Save my Exams - IG,IB,GCSE,A level,AS level,O, Pre U