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Headings
HTML has six “levels” of headings:
1-< h1 > is used for main headings.
2-< h2 > is used for subheadings.
3- If there are further sections under the subheadings then the < h3 > element is used, and so on…

Paragraphs
< p >
To create a paragraph, surround the words that make up the paragraph with an opening < p > tag and closing < /p > tag.
Bold & Italic
< b >
< i >
Superscript & Subscrip
< sup >
The < sup > element is used to contain characters that should be superscript such as the suffixes of dates or mathematical concepts like raising a number to a power.
< sub >

White Space
When the browser comes across two or more spaces next to each other, it only displays one space. Similarly if it comes across a line break, it treats that as a single space too. This is known as white space collapsing.
Line Breaks & Horizontal Rules
< br />
As you have already seen, the browser will automatically show each new paragraph or heading on a new line. But if you wanted to add a line break inside the middle of a paragraph you can use the line break tag < br />.
< hr />
To create a break between themes — such as a change of topic in a book or a new scene in a play — you can add a horizontal rule between sections using the < hr /> tag.