Book excerpt: Mathematics has always been my ‘weakness’. By weakness today I mean that I am in love with it. But I literally felt weak in my head also, when I was first introduced to – Calculus! Practice, practice, and more practice…there is no other way out. But often I felt if only I had a sort of handbook, a type of ‘dictionary’ (you know what I mean…) that would lay down the important features of the topic in a precise way, one after the other. I searched the internet and watched many videos on YouTube, and over and above I had one of the best Mathematics teachers in Army Public School, Kolkata: Mrs. M. Kathuria. With her help, I slowly tried to get a hang of this dreaded topic of Calculus. I am not sure, yet, how much I have succeeded, but I have managed to write this book. It is a brief description, a definition of sorts, of the main structure of the topic. I hope you guys like it and find it helpful. All the best!