The paragraph tag defines a block element. After each block element a new line occurs. The text in this block has been defined by a p tag.

The h5 header tag defines a block element. After each block element a new line occurs. The text in this block has been defined by an h5 tag

However, the em tag (which is used for emphasis) defines an inline element. Here I use the tag to emphasize these words. Notice that a new line doesn't happen after it's used.

h6