How to use <h1> <h2> <h3> <h4> <h5> <h6>?

creates the level 1 header. creates the level 2 header, etc.

Example

 This is a #1 heading
 This is a #2 heading
 This is a #3 heading
 This is a #4 heading
 This is a #5 heading
 This is a #6 heading