As we discuss before that HTML have syntax
Mean every tag which we start need to be end
<tag> is Start Tag syntax and </tag> is END Tag syntax
We start from HTML tag <HTML>
We always start HTML page from html tag and also end it at HTML Tag.
In between we write our HTML page other tags according to our requirements.
Why we use it?
Actually we use HTML tag in start of file so that browser can understand that all code in between is following the HTML syntax.