Heading tags are an important part of your page's SEO.  Search engines look at text in your heading tags to get a better idea of what your content is about.  Using heading tags correctly can help your SEO.

To add a heading tag:

1.  From the left menu of the Editor, click Add.

2. Select Text.

Here, you can drag the title that you want onto your page.  Each title is mapped to a heading tag:

• H1 - Site Title
• H2 - Page Title
• H3 - Section Title
• H4 - Title 1
• H5 - Title 2
• H6 - Title 3

There are no restrictions as to how many heading tags you can add.  Generally, you should use titles according to their function and place titles where it makes sense.  Abusing the use of titles may confuse not only your visitors, but also search engines.

Although heading tags are categorized from 1 to 6, there are no restrictions to their design -- that is, H1 doesn't necessarily need to be bigger than H6.  The number is just used as hierarchy of importance, meaning H1 is more important than H6.