A structure type is usually defined near to the start of a file using a typedef statement. typedef defines and names a new type, allowing its use throughout the program. typedefs usually occur just after the #define and #include statements in a file.
Here is an example structure definition.
typedef struct { char name[64]; char course[128]; int age; int year; } student;
This defines a new type student variables of type student can be declared as follows.
student st_rec;
Notice how similar this is to declaring an int or float.
The variable name is st_rec, it has members called name, course, age and year.