Here are the basics.
The br code before this sentence made a line break.

The p before this one made a paragraph break.

Using two blank lines also makes a paragraph break.

This text is bold.

This text is centered.

This text is italic.

This text is underlined.

This text is size 1.

This text is red.

This text is also red.

This text is size 6 and green.

This is a header.

This is ComicSans text.

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This is a bulleted list!

• Item one
• item two

Here is how to divide your page with a horizontal line: