How can we use <h1> tag in on-page seo? And what is the benefits of <h1> tag ???

It's for headers. Use it for article titles at the top of a page. 'Nuf said.

h1 tag is header tag.
thanks

H1 Tags is used for the header to summarize the content of your website. It helps the search engines to easily understand whats your website is all about so that it will appear on the search engine result page when a particular keyword was searched.

ya i agree with those sayings of weboutgateway and thanks for sharing those nice info

The text is in heading because it is more important for the web page and Google fetch the easily the website which have some heading tags.

Benefits of using heading is that search engines generally give priority to keywords taht are formatted with the H1 or H2 Tags, because the use of a heading tag implies that the text has greater importance on page.

It is used to define the content of the page and for proper document layput.Google easily fetch the websites having heading tags.