The header tag, or the <h1> tag in HTML, will usually be the title of a post, or other emphasized text on the page. It will usually be the largest text that stands out. There are other header tags in HTML too, like an h2, h3, h4, etc.
Heading tags, as the name implies, are tags that are used for the creations of headings. The most important tag is the <h1> heading tag, and will usually be the title of a post. Heading tags have a top-down hierarchy from <h1> to <h6>. There are two ways heading tags can structure your content.
Header tags are an important on-page SEO factor because they’re used to communicate to the search engines what your website is about. HTML Tags are used for giving headings. H1 is the first heading which is the most important while H6 being the least.
Heading tags are HTML tags used to identify headings and subheadings within your content from other types of text (e.g., paragraph text). The hierarchy goes from H1-H6.