HTML Paragraph tags are very important, the html documents are divided using paragraphs.
Try typing two lines of words with HTML paragraph tag and two lines of words without paragraph tags and see the difference.
HTML Paragraphs Example
<p>This is Line 1</p> <p>This is Line 2</p> This is Line 3 This is Line 4
The Lines with out paragraph tags will be displayed next to each other. Even if you type them in two separate lines, the browser will consider them as a single line.
Browsers will automatically add some space before and after the paragraphs, the amount of space depends on the type of browser.