Block-level elements like (<div>, <pre>, <p>, <ul>, <ol>, <li>,… ) take up the entire width of their containing element and the height of the default line-height. They stack up underneath each other, top-to-bottom.
Inline elements like (<img>, <em>, <strong>, <a>, <span>, …) are in-line. They stack up next to each other, left-to-right.
All HTML block-level elements have five spacing properties: height, width, padding, border and margin. In the HTML box-model, the width of padding, border and margin are added to the width of the content area.
Applying float to an element will automatically make it a block-level element.