/sci/ - Science & Math

How do I start solving this?
I took a course ''Standard Model of Elementary Particles''. I thought we would be talking about particles, them interacting with each other and matter, about their properties and how they were discovered and how they can be detected.
Instead I need to do some Lagrangian math that I don't understand and don't see the purpose for.
I will probably just google answers or find them in the textbook. But how would I start with solving something like this? Btw, would greatly appreciate if you also guided me into where I can find the answers for this.