What the tag!

Hey all Im doing some customization on Dolphin I promise I will share my codes once I had them finished, it has been hard...Im still trying to figure what this kind of tags have their origin on

__promo_code__    __include_header.html__ and so on....

Every time I figure it out something changes and its not the same... being part of the templates (i.e) I want to add another CSS on the __header.html but I don't find the source or a class that helps me with the configuration...can anyone put me on the rite direction?

because I want to have a customized Index instead of the main homepage that dolphin had configured...

thanks a lot...

Ah! like dosdawg said: putting the exact words for something can be more helpful well I did! and I searched "custom Index" and the result is

http://www.boonex.com/trac/dolphin/wiki/GenDolFAQs

And thats exactly what I wanted to do. And also I could figure what the __damnned_tags__ mean.

The above are the template keys.

Can you plz. explain what you are looking for.

Yeah

What Im looking for is to create my own dynamic code, for example my own index or another block with dynamic code.

For example with the index I want it different I don't want the hole screen just the Login and Join Features, like this
I studied the code and yes are templates tags and they origin from variables like this ones $_page[] or for this example $aFormReplace[submit_label], but It doesn't seem to work I know Im missing something...

Page builder doesn't work for me, I can't create New Blocks Or Items and I decided to go manually but the code is a little bit confusing...

Thank you for answering