What are the differences between 'URL','src' and 'herf' ?

Answer 1

SRC is an attribute use for image,
HREF is use for link

Answer 2

URL is always set on CSS to define a source of a file.
#mydiv {
background-image:URL("the path for the background image goes here");
}

SRC means source, it does the same thing that URL does, but, is always set on HTML.

<img src="path for the image goes here">

HREF is used to set a link on a element of your page.
<a href="page.html">If you click here you will be redirected to "page.html"</a>