You know what FTP stands for, but you admit to not knowing its purpose...
A FTP program creates a connection between two computers on the internet, allowing an exchange of files between the two machines.
There are some FREE FTP programs (filezilla), but I use a commercially available program called WS-FTP-PRO, made by a company called Ipswitch.
My reasons for choosing this paid-for software over the free Filezilla, is largely for better security and more enhanced (and safer) features.
Because CMS websites operate using code files and a database, you need to understand the relationship between the CODE FILES, and the DATABASE in which a large portion of your site's content is stored.
The FILE SYSTEM and the DATABASE are two completely separate "entities" in a CMS website. Think of these as two "linked branches" that interface with each other, in the process of compiling your site's web pages, which your visitors ultimately see on their computer screens, and which they use to get the site to "behave" in a desired way (such as adding a product to the shopping cart).
The FILE SYSTEM is a complex array of code files that contain "instructions" to govern the behaviour of the site. When a page is called up on a browser, the PHP gets busy assembling all the bits that are needed, according to the "request" being made. It gathers these up from what can be hundreds of places - many of them in the database, others in additional code files, and yet even more (eg: images) from "storage bins" (folders) where they are patiently waiting to be included on a requested page.
The DATABASE is the repository of most of the information (data) that the site needs in order to render pertinent information - such as the description of a product, its price, and its configurations (it may be a shirt that is available in several sizes).
Because the data can be (and indeed is) used in many different parts of the site, it makes good sense to have only "one version" of it, so a 100% reliable piece of data can be called up to take its place on a page. For example, a product TITLE can appear in a product listing, a search result, a product info page, the shopping cart, an order history, an email confirmation.... So you want to be sure that the product TITLE for any given item is accurately rendered every time it is needed.
The PHP will call up the same piece of data, and depending on what that bit of PHP is being expected to do, it will render the single piece of data (product title) in ALL instances where it is needed.
So your web pages are what we call DYNAMIC... They are created when needed. The php assembles a page, and delivers it to the viewer's browser screen.
When they click a link, or a button (eg: Add To Cart), they page they are viewing EVAPORATES forever, and an entirely new one is assembled and sent to the browser. In many cases, an ACTION is performed along the way - when Add To Cart is clicked, not only is a NEW page assembled, but bits of information are added to the database, or "flagged up" as being relevant to a transaction or "event". This is then in "memory" and can be re-called for later uses.
PHP FILES
Sometimes, it is necessary to make edits to CODE FILES. You may wish to change a LABEL, or a phrase of text - or perhaps ajdust some layout features.
When a php FILE needs editing, a COPY of the relevant file needs to be transferred from its place on the server, to your home computer. It can then be opened up, and edits can be made.
As the edits are made on a COPY, the ORIGINAL file is un-touched, so it retains its original behaviour.
Before you send back your EDITED version (via FTP), it is advisable to rename the ORIGINAL file to .bak (as opposed to .php, so that you have a "backup" of the file which you can revert to if your edits contain errors.
There is more to it - such as the over-rides system - but I'll leave that for now... The above needs to be digested first! :D
