Google and other major search engines gives importance to the header tags in the following order.

h1 tag
h2 tag
h3 tag
h4 tag
h5 tag
h6 tag

First prioriy is given to the h1 tag because the h1 tag shows the theme of the topic discussed in the page. As a wel orgganized web page is oriented on the single topic usage of h1 tag on a page is limited to 1. If we use more than one h1 tag on the same page it may lead to google penalty.