Dive into the fundamentals of particle physics, Lagrangians, and Feynman rules in this comprehensive lecture from the ICTP-SAIFR/ExoHad School on Few-Body Physics: Nuclear Physics from QCD. Delivered by Felipe Ortega-Gama from Lawrence Berkeley Lab, USA, this 1 hour and 38 minute session serves as the first class in a series exploring the intersection of nuclear physics and quantum chromodynamics. Gain insights into the basic principles of particle physics, understand the importance of Lagrangians in describing physical systems, and learn how to interpret and apply Feynman rules in particle interactions. Perfect for students and researchers looking to strengthen their foundation in theoretical physics and prepare for advanced topics in nuclear and particle physics.