Important HTML Tags

I was going through the html course in W3schools then
I find some important tags which i had never used in html, so
here are these tags :
<small>
<del> // delete with line
<ins> // insert in stead of delete
<mark> // gives color to text
<cite> // Title of the work
<q> // Short Quotation
<map> // tag is used to define a client-side image-map.
An image-map is an image with clickable areas.
<fieldset>
<optgroup> Group related options with <optgroup> tags:
Autofocus in <button>
<datalist> //An <input> element with pre-defined values in a <datalist>
<noscript> text when javascript not supported by browser! </noscript>