In C programming, structures (also called structs) are a way to group several related variables into one place.
Each variable in the structure is known as a member of the structure. Unlike an array, a structure can contain many different data types. The different variables can be accessed via a single pointer or by the struct declared name which returns the same address.

Declare a Structure:
The general syntax for a struct declaration in C is:

struct name {
    type member1;
    type member2;
};

Initialize a structure:
Let's assume that we have a structure named player declared as follow:

struct player {
    unsigned int height;
    unsigned int width;
    unsigned int health_point;
};

You can:

.Define a variable p1 of type player and initialize its members according to the declaration order in the structure as follow:

    struct player p1 = {800, 600, 1200}; 
                /* OR */
    struct player p1 = (struct player){800, 600, 1200};

.Use designated initializer style to access each member in a random order:

    struct player p1 = {.health_point = 1200, .width = 600, .height = 800};

Note: If an initializer is given or if the object is statically allocated, omitted elements are initialized to 0.

.Copy the value of an existing object of the same type:

    struct player p2 = p1; /* p2 will share the same properties as p1 */

Source:
Wikipedia

Best resources to study this topic:
GeeksForGeeks
OpenClassroom
C advanced doc - DevDocs