What is the difference between title and the heading tag ?

Both tags should provide titles that represent the overall message of your webpage, so the best way to optimize Title Tags and H1 Headers is to write for your readers, while following SEO best practices.

Main Differences:

• Title Tag is a meta tag: it's in the head of the page, that is not part of the actual content. You won't see the title tag on the page, other than at the top of your browser screen. 
• Title Tag a hint to Google what your page is about.
• Title Tag is shown in the SERP as the link searchers click on to visit your page.
• Heading Tag is visible on the page. In other words. It's usually the most prominent text, and tells a visitor what to expect on that page.

Common Best Practices:

• Try to place the keywords early in both tags.
• Use only one H1 Header per webpage.
• Avoid keyword stuffing: use the keywords only once within each tag.
• Include the page’s primary keywords in both tags.
• Keep both titles short. (50 characters or less recommended)

The Title composition guidelines:

• The headline should be catchy enough to catch the user’s attention.
• The recommended number of characters is 60-70. More characters will not show up in Google's SERP.
• Place significant keywords closer to the beginning of the Header.
• The dilution of the main queries with low-frequency queries is allowed.
• The use of question enumeration is not recommended.
• Transactional words like buy, order, price, and so on should be used.
• The title must motivate the user to go to the website.

The H1 composition guidelines:

• The H1 Header can be used only once on the page.
• The length is usually up to 50 characters.
• The H1 subject intersects exclusively with what is discussed in the text section.
• You can’t over spam with queries.
• You can use a frequent question that did not fit in the title.