In C programming language, declaring a variable involves specifying the data type and the name of the variable. To declare a variable in C, the syntax is as follows: “data_type variable_name;” Here, “data_type” refers to the type of data that the variable can hold, such as int (integer), float (floating-point number), char (character), and so on. “Variable_name” is the name given to the variable, which can be any valid identifier consisting of letters, digits, and underscores. It is important to choose a meaningful name that reflects the purpose of the variable. For example, to declare an integer variable named “count”, you would write “int count;”. Additionally, multiple variables of the same data type can be declared in a single line by separating their names with commas. After declaration, variables can be assigned values using the assignment operator (“=”) to use them in the program.