The purpose of URL's is to uniquely locate and identify things on the Internet. Primarily these things are web pages, and for this discussion that's all we'll talk about. The principle use for URL's is to be a kind of address at which you locate a web page, just like "123 Maple St." might be the address for somebody's house.
The leading part, the "http://" is technically very important. However, the web browsers make it possible to ignore this part and go directly to the rest. The rest begins with a name for a computer, in the case shown "www.amazon.com". Somewhere out there on the Internet is a computer named "www.amazon.com", and by the magic of technical wizardry your act of typing the address into the location bar of a web browser causes Internet traffic to be sent to and fro between your computer and that one.
The general syntax for a URL is
scheme://authority/path?query
The scheme is basically the method of reaching the thing being identified. That is, http or https are the methods, or schemes, by which the majority of web pages are retrieved. The authority typically is the hostname for the computer from which to retrieve the thing. The path further specifies which thing within the things held by the authority computer. The query portion is sometimes used to pass parameters to software, for example to look up an article ID in a database.
For someone building a web site your URL will be:
http://www.example.com/
Your web building software, whatever you choose to use, will organize a hierarchy of pages and images. This hierarchy is directly represented by a hierarchy of "folders" within your computer. For example it's typical that when you have a series of articles on a given subject, to create a folder to store those articles. Then the topic folder would end up containing all pages and images related to the given topic.
For example, if you want to write a series of articles ranting about Microsoft Word, your folder structure might be like this:
.../
software/
msword/
rants/
index.html
death-to-clippy.html
bloated.html
incompatible.html
The resulting URL might be this:
http://www.example.com/software/msword/rants/death-to-clippy.html