return-Type   functionName ( formal-parameters )
   {// function-body 
       local variables definitions

       statements
   } 

Example: function that returns the square of a number

   float square( float x )                  
   {
      float r;         // Define a local variable         

      r = x * x;       // Statement
      return ( r );    // Return statement
   }

Meaning:

C does not have instance methods (instance methods works with objects and always use a implicit parameter (this))

C functions do not have implicit parameters I.e.: all parameters of a C function are listed in the parameter list of the function