Underline is a formatting element used to represent different text form other. It indicate that the text is misspelled or represents proper noun in Chinese language. It is used to define underlined text means it gives horizontal line below any text where it is applied.
<u>Content</u>
Or
<tag><u>Content</u></tag>
You can apply underline element to any element and use any where within a HTML document.
Underline is a pair tag and output of underline element is horizontal line below text like you can see in above example.
Open notepad or any other text editor, follow the following points.
save file with name task.html or task.htm and then open it using any browser and see results.
Don't forget underline is non empty element which means it always comes in pair.