I'm looking for some resources (article or videos or courses) to understand the working of Illumina and other NGS platforms? I have a lot of concept gaps and doubts.
Your gaps and concepts would/could have already been solved if you have searched the exact heading of your question in your browser. Also, there are hundreds of discussion are available even here on researchgate.
I recently came across this post https://kscbioinformatics.wordpress.com/2017/02/13/illumina-sequencing-for-dummies-samples-are-sequenced/ and it does a decent job explaining it I think.