I am new in SEO Field. So please anybody give me some information about H tags - H1,H2,H3,H4,H5,H6 .

page should never be long enough to warrant using H5 and H6 tags - so for optimisation purposes, the H tags you will use are H1 to H4.

When using header tags correctly, after the H1 tag, the next header element used should be the H2 - Don’t ever jump from H1 to H3- The search engine spiders need to see a natural progression down the page. That doesn’t mean you cannot have more than one H2 tag; there is no issue if the progression goes H1, H2, H2, H3, H3, H4. Simply use the headings to separate subjects related to the importance of the information, as you would naturally do when writing any information page:

H1 This is the main thing I’m optimizing for and the overall introduction to the content of the page.
P Paragraph
H2 This is the most important aspect of the subject of this page
P Paragraph
H3 You should also be aware of this
P Paragraph
P Paragraph
H4 and finally….

Hope now you understand...