Customizing a single page in wordpress custom template

Let me start by saying I am completely uneducated in the ways of css, php, codex and all html website coding… I don’t even know what those things are I just mentioned. So please if you can help, I need you to walk me through as if I just learned how to turn on a computer — when it comes to web design.

I want to customize a singe plage in my wordpress theme

http://www.thetitancorps.com/store/

I need this page to be wider in the gray area where I can put items for sale on this online store. I’ve asked this question before and I am always referred to the developer. People say, “you have to check with the developer on how to customize that page.” The problem is, I can’t get in touch with the developer! It’s an older theme and there is ZERO customer support available. What I need is a patient wordpress pro that can walk me through what I need to do.

I’ve researched online how to create a “custom php” then customize your one page for your theme. I found two web links with good info, but I am completely lost how to do this. I don’t know how to create a blank PHP nor do I have any idea how to turn it into a working page for my theme. Here are the links I am talking about:

do this:
http://line25.com/tutorials/how-to-create-a-wordpress-custom-page-template

then this;
http://premium.wpmudev.org/blog/create-a-full-width-page-for-wordpress-in-5-simple-steps/

Can anyone tell me how to get this done — please I have no where else to turn!!!

– William