What <div> or </div> tag and for what and why it is used?

Answer 1

It makes "block".
For example if you have article then you want to have block with header of article and block with content then you will probably do:
<article>
<div>
Title
</div>
<div>
Content of article.
</div>
</article>

It is useful for identify block from website in CSS sheets. You can make <div id="headofarticle"></div> and make visual concept of this block in CSS only for this div.

#headofarticle {
color: #FFFFFF
}

Answer 2

what is full form of div tag

Answer 3

There are a lot of options for div. I think (but not sure) the most valuable are id= and class= and maybe style= if you want to edit visual concept of it in html not CSS.

Answer 4

check this as a sample of using div

https://code.sololearn.com/WNvSp3Q9S5GD/?ref=app