why use the relative in css code example

Example: relative positioning html

/*position: relative;
An element with position: relative; is positioned relative to its normal position.

Setting the top, right, bottom, and left properties of a relatively-positioned
element will cause it to be adjusted away from its normal position. Other 
content will not be adjusted to fit into any gap left by the element.*/
div.relative {
  position: relative;
  left: 30px;
  border: 3px solid #73AD21;
}