ok guys  i show you what is html element. between the start tag and the end tag the html element is there. in html tag there should be many element and that is called nested element.just see the exmple
<!DOCTYPE html>
<title>this is page title</title>

    this is unorder list

<h1>demo heading</h1>
<p>demo content goes here.</p>
look on the html start and end tag. between that many tag or we can called that element.in the element there should be more element.such as in the above example the ul is a element of an element. as there should be content on a element such as the h1 is a element and in that element there is the content. and with that content the whole thing is element of html. be attention when you write the code dont forget to end the tag. remember one thing you have to write all the code on body. the output comes from there.
now guys there have two kind of element. such as
1)block level element and
2)inline element
block level element:
the answer is which element contain all space on its right or left on default. those element which start a new line. such as div, p, h1, ul, li etc.
now inline element:
which element doesnot start a new line in browser. such as a, i, b, span, strong etc.