why display block in css code example

Example 1: css block layout

/******************* BASIC BLOCK DISPLAY **********************/

/**************** Block display Elements  *********************/
/*Elements that block any other elements from being in the 
same line. You can change the width from being the maximum 
width of the page, but you can´t put elements side by side */
tag_name {
    display: block;
}

/*Exemple of default block display elements:*/
 ... 
 ... 


/**************** Inline display Elements  *********************/
/*They are the type of blocks that only take up the minimum space 
required (both in width and height). You can place these types of 
blocks side by side (on the same line) but you cannot change their 
dimensions */

tag_name {
    display: inline;
}

/*Exemple of default inline display elements:*/
 ... 
 ... 
 ... 


/************* Inline-block display Elements  *****************/
/*They take the best of the two other types above. You can put 
elements side by side (on the same line) and you can change this 
block width and height */

tag_name {
    display: inline-block;
}


/***************** None display Elements  ********************/
/*This block will never appear on your webpage and will never 
interact with the other elements (it doesn't take up space) */

tag_name {
    display: none;
}

Example 2: display: block;

p.secret {
  display: block;
}