Each type of element displays in a different way, as explained below. This is why CSS has a display property. With the display property you can, theoretically, redefine the display type of an element. Instead, they use the display type as specified by the W3C's HTML recommendation. See the browser compatibility information for the display type property for information about current browsers in this regard.
Browsers generally give block elements a standard margin to the top and bottom.
With cascading style sheets, you can redefine the margin around block elements. Inline elements are not separated from surrounding elements in the flow, but rather follow directly on from their adjacent elements. Inline elements display just as text does on a page. With style sheets an image can be specified as the marker, and different types of marker, in addition to the common disc and square, can be specified. Which makes sense if you think about it.