Web pages usually contain paragraphs. The main purpose of the HTML5 <p> tag is to determine the paragraph within the HTML document. This is necessary so that proper margins and spacing in between the paragraphs can be added in the document, making it easier for the users to identify the partitions.
Formatting the text and paragraph which are placed in the HTML5 <p> tag can be done through CSS.
The HTML5 <p> tag is used differently in HTML4.01. In HTML4.01, the align attribute can still be used but this is no longer adapted in HTML5.
The good news is that using the HTML5 <p> tag is not going to ruin the look of the document since this is accepted in all major web browsers like Safari, Internet Explorer, Google Chrome, Firefox and Opera. Aside from that, the HTML5 <p> tag is also compatible of the Event Attributes and Global Attributes in HTML5.