Text formatting enhances its look & feel & makes a webpage more attractive.
HTML has following formatting tags:

1) <b> : Makes text bold
2) <i> : Makes text slightly tilted
3) <u> : Underlines the text
4) <em>: Makes an emphasized text
5) <mark>: Highlights a text
6) <del> : Shows a deleted text
7) <sub> : Shows a subscripted text
8) <sup> : shows a superscripted text
9) <ins> : Displays an inserted text
10) <small>:Displays a small text
11) <big>: Displays a big text
12) <strike>

Making text bold with HTML tag

Example:

<html>
<body>
<b>This is bold text</b>
</body>
</html>

Making text strong with HTML tag

Example:

<html>
<body>
<b>This is strong text</b>
</body>
</html>

Making text italic with HTML tag

Example

<html>
<body>
<i>This is italic text</i>
</body>
</html>

Making text emphasized with HTML tag

Example:

<html>
<body>
<em>This is italic text</em>
</body>
</html>

Making text small with HTML tag

Example:

<html>
<body>
<em>This is SMALL text</em>
</body>
</html>

Mark or Highlight text with HTML tag

Example:

<html>
<body>
<mark>This is Marked text</mark>
</body>
</html>

Strikethrough or delete text with HTML tag

Example

<html>
<body>
This is <del>deleted</del> text
</body>
</html>

Subscript text with HTML tag

Example

<html>
<body>
<p>This is H<sub>2</sub>O</p>
</body>
</html>

Superscript a text with HTML tag

Example

<html>
<body>
<p>This is a<sup>2</sub> </p>
</body>
</html>

Insert or add a text with HTML tag

Example

<html>
<body>
<p>This is <ins>inserted</ins> text </p>
</body>
</html>