how to mod?

[xQdcss]

Where I can find the properties of everything in half life 2?I wanna make a mod on half life 2 engine but I dunno how to find the .cpp files or whatever they are called
Note:I only own Half life 2 not the episodes so I think I am able to make a mod from this am I right?
But things are worse....when I go to Source SDK,select 2009 engine, click create a mod then it tells me "Support for creating total conversions are not available using this engine versions"...I changed to 2007 and then the option to create a singleplayer mod for hl2 is greyed out and then I tried with 2006 and that option isn't greyed out but I don't want to mod on this outdated engine I wanna 2009 engine how do I do that too?
And I don't need a team for my mod I know some C++ and I think that's enough I just to do some little coding for my maps that's all

[Gary]

2009 engine is closed source. We have no access to it's codebase. Sorry, all you can do is create maps and assets for it(just like Portal1/2, L4D1/2, TF2, and DOTA2 will be).

2007 is what all modern mods use, with the few exceptions. Codebase access.

2006 is the ep1 codebase, outdated. Only old mods use this. Codebase access.

ASW(AlienSwarm), the engine is better than the 2009's, but the codebase is in most cases not. Little support and everything is setup for top down perspective. Codebase access, no custom shader support unlike 2006/2007.