so firstly i recommended that see my previous lecture about lambda calculus on my channel that make help you for more understanding to this topic.
lambda calculus introduction • PPL1.1-Lambda Calculus | Introduction | pr...
lambda Abstraction and Free/Bound Variable • PPL1.2-Lambda calculus | Abstraction | Fre...
Ppl Principle of Programming language Topic-substitution and Beta Conversion and also Include Alpha and Eta Conversation or Reduction .