Here, I will add links for web pages where I have written about concepts from Kobayashi and Nomizu's book Foundations of Differential geometry (Volume \(1\) and Volume \(2\)). Derivative of Left invariant differential form Maurer-Cartan form on a Lie group Transition maps for principal bundle are smooth Trivializations and sections in Principal bundle Construction of Weil homomorphism Construction of associated bundle Equivariant maps are Isomorphisms Invariant polynomials