Help me to get the knowledge.

[Mitch]

- Are those all avaible build-in functions, natives, server variables? - https://znation.nl/cod2script/
The cod2 + libcod documentation only contains functions and player/entity methods.
All cod2 functions are complete, but newer libcod functions take sometimes a while to be added.
For basic scripting (variables, map structures) take a look in iw_07.iwd or/and iw_15.iwd (1.2/1.3) and go to maps/mp and maps/mp/gametypes.

- Is libcod the external support created by the community?
More like an extension to have new features and fix some old bugs. I guess it is.

- How do I include it to my future projects? ( export LD_PRELOAD="$HOME/cod2_1_0/libcod2_1_0.so" ) ?
Use your own sh script or wrap the stock binary like this (link) and use any controlpanel you like.

- How the server is build ( based on the files - main and the includes )? Is there a core file or it's all based on the maps?
All iwds are loaded in ordered by name, first main and then fs_game directory.
You can see the order when the server starts in the console log.
Loaded files are overridden by files loaded afterwards.

- How do I connect all my scripts into one mod? How should I separate them for example to make a mappack or additional mods.
For 1.0: in one iwd (in fs_game dir) or placed in fs_game directory in the same map structure as in the iwd.
The gametype file must be in the iwd used by the clients to load the gametype text (or some other reason)
(1.2?)/1.3: z_svr_*.iwd is not downloaded by the clients.

Mappack were made in the past to get more maps on the server without reaching the iwd cvar string limit.
But with libcod you can load and unload maps with manymaps feature (link).