You don't need to read this. Really. If you are the sort of person who can drive a car, but has no real clue as to what goes on in the engine, and you have no desire to enrich your life with the finer details of the internal combustion engine, then feel free to ignore this page. WordPress won't know you don't know, and it will still work if you just follow the guide for your client.
If you do want to know a tiny bit more, read on. It is only a tiny bit though... a mere morsellette if you will.
CHMOD stands for CHange MODe.
You upload a file, then you change it's mode. It's also known as altering it's 'properties' or 'permissions'.
Q. What is it, and why do I need to do it ?
Servers, where your WordPress installation is, need information from you about how to use the files that you have uploaded. The language they use for this is not like anything that you have installed on your computer, unless you use Linux in which case you don't need this guide anyway.
It's a complex subject, and involves talk about Unix and other software environments. I'll skip all the complex stuff.
Q. Why CHMOD ?
Because the server needs to know who can do what to your files. Remember, computers do exactly what they are told to do, so this is all about giving it instructions as to how to behave.
Now if it's it's an HTML page, or an image, then there's not a lot anyone can actually do to them except view them. But if the file is a script (php / javascript for example) then you can tell the server who can use the file, and who can alter the file. If it's a folder, you can tell the server who can put things into that folder.
You want to be able to access and run all your files, you want people who visit your site to be able to add comments / posts / images, but you don't want someone to be able to hack in and change all your stuff around.
With me so far ?
Oh yes, and unless you do, your WP install won't work.
Q. How does it do this ?
By assigning a number to each file.
As you'll see in the tutorials, certain numbers give certain permissions. Some FTP programs will have you check a combination of boxes to set the numbers, some ask for the number to be directly typed in by you, and others allow both.
Q. How does it work ?
There are 3 actions that can be carried out on a file/directory. You can;
READ it
WRITE to it (also called modify)
EXECUTE it (that is, run it)
When the server goes to access a file or directory, the first thing it does is check it's number. It then compares the number to what or who is asking and what they are wanting to do.
If everything matches, then the action will be carried out.
If it does not, an error will be generated.
Q. Okay ... so this means what then ?
I said I'd leave out the complex stuff.
It means that by setting the required permissions, you are securing your install against someone else messing it up. I may know the directory that would have installed WordPress into (don't most people have a /blog directory ?), but even with that information, and knowing how a WordPress install works, I cannot alter it in any other way than by posting comments to your page.
Q. This CHMOD sounds like great fun ! Where can I learn more ?
May I suggest you go for a lie down in a cool dark room for at least a hour or until this notion passes?