The tutorial clearly states you use the custom only if you have a custom and that custom represents the override, NOT that it is reserved.
I hesitate to suggest that you are jumping on your horse and riding madly off in all directions rather than taking time to plan the trip.
The link I gave you for the override tutorial specifically states how to create an override directory. After you started this thread, I specifically went back through each thread in the tutorial as I setup a new site. I put on my "pick it apart" hat and followed step by step in sequence starting with loading a fresh install, creating the override directory, and removing the "offending" passages from english.php, index.php and meta_tags.php.
It MIGHT be possible that someone could misconstrue the text in the tutorials, but I humbly submit that my guess would be the "skimming" culprit. We see it on the forum all the time. Many hit the highlights, ignore the docs folder, and skim the tutorials. Next they search the forum without having learned the terminology of the beast. Is it options or attributes, custom or override, admin or backend? If I'm not familiar with the terms, I try to absorb them before deciding the instructions are incorrect.
There HAVE TO BE several directories and files in order to have an override. And then, you still need to go into your admin(backend/main control) and select the template. You will accomplish little by simply throwing in a css file without creating an override.
If you purchased a template (notice I didn't say css) I hope you didn't get one from Template Monster or one of their affiliates. If so, that could well be adding to your frustration right now. Regardless, you should have received instructions with the template and it should have come with a file structure that must be followed to work at all with Zen Cart. Don't care how fancy the car, it's hard to drive it without knowing where the steering wheel, gas pedal, brake, and gear shift are located.
As for the blank page when you modified the meta_tags folder; did you search the forum for blank page? It normally means that you've made an error in editing and dropped an important apostrophe somewhere along the way. A define statement has two apostrophes. One at the beginning of the define and another at the end. Common mistakes are to delete something (like Zen Cart! The Art of e-Commerce) and also delete one or both of the apostrophes. OR... Changing the Zen Cart tag to something like 'We're the bestest!' without making it 'We\'re the bestest'.
Also, since 1.3.9 started replacing 1.3.8, the system has included a debug system that drops a file that starts with debug into the cache folder of your site. You might want to look for the cache folder and see what files are there.
In short
, I think you need to quit standing in front of the microwave hollering "HURRY UP!" Multitasking is not a good thing when setting up a cart. Stop at each phase and check for accuracy and completeness. Learn the lingo. Figure out how to "order a beer, a steak, and get @#@#)" in this new language. That's what I'd do if I found myself in Greece.
It's early in your process. I'd start over fresh, do the override (with or without your template) and s l o w l y work from there.
Most everyone on this forum has been in your shoes and all of us have tried to hurry through some part of an installation. We generally wind up with
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