This lecture covers the fundamentals of variables and types in the C programming language. It begins with the definition of a variable, highlighting its three main characteristics: identifier, type, and value. The instructor emphasizes the importance of using explicit names for variables and adhering to naming conventions. The lecture explains the initialization of variables, noting that unlike Java, C does not automatically initialize variables, which can lead to undefined behavior if not addressed. The syntax for declaring and initializing variables is presented, along with examples of basic data types such as int, double, and char. The concept of modifiable and non-modifiable variables is introduced, explaining the use of the 'const' keyword to create read-only variables. The lecture also discusses the assignment operator and its semantic differences between C and Java, clarifying how assignment in C involves copying values rather than referencing objects. Finally, the instructor summarizes key points about variable characteristics and types, preparing students for more advanced topics in C programming.