This tutorial aims at providing solid ground to develop out-of-tree LLVM passes. It presents all the required building blocks, starting from scratch: cmake integration, llvm pass management, opt / clang integration. It presents the core IR concepts through two simple obfuscating passes: the SSA form, the CFG, PHI nodes, IRBuilder etc. We also take a quick tour on analysis integration through dominators. Finally, it showcases how to use cl and lit to parametrize and test the toy passes developed in the tutorial.