Well, I finally got my map to load from the mod list.
First I load mod then start game.

I wish I understood it more though.
So what I'll do is explain it the best I can and
then anyone can comment me on what is wrong and what is
right or what I forgot.
Also feel free to explain what things are doing.
Here it goes.

my_mod is the folder everything sits in.
description.txt will bring up the name of the mod in the hud.
.def's are definition files they can be used for alot of stuff
like changeing numberofrounds in pistol,damage done with pistol and a whole lot more.
Wish I new more about them so I could alter more things.
my_mod say is My first mod will load and run without .def files.
So why do we create a write a my_mod.def ? with saying what kind of map say single player and all that size stuff.
what's size all about anyway?

moving on...
now I think the reason my_mod is running without a .def is because I rewrote mainmenu.gui first I load mod then I start game and there's my level.

but I would like to know how my mod could load once I click on the mod from the list automatically?
though it now works this way and if you don't load mod from list and you start the game you get doom 3's first level on mars.

.pk4 looks like they hold .def's,.gui's, picture files sound ect.

my .pk4 has nothing in it my_map is in my_mod/game/my_map.map
So what do I do put into a .pk4?
custom textures and sounds

That's about if for now
Please fill me in I would love to know more
understand more
exactly what things are doing and what not

Thanks
DeathStalker
otherwise known as Scott B.

I'm glad you got it.

comments on your post:

- you don't write my_mod.def for you mod. But you do write my_map.def for your map. this tells the game what your map is good for such as singleplayer, dm, ctf, etc.

- size is used for the loading screen (That's all I know of). That loading bar at the bottom will work if the size is inserted correctly. Each of the 4 sizes is based on the lower to higher video setting in the game. Sometimes higher quality textures are used for hight quality video settings.

- I never thought of loading your mod immediately. That would mean that someone could save their game and go back to load it. There would be no opening screen for your mod. Aside from that, I guess you could do it by creating a new GUI for the first screen of the game. Remove all the graphics and everything. Then write a script in there that loads your first map immediately.

- pk4 files hold the entire contents of the game. That content is loaded unless you create a new one in your mod folder. You could extract all those files from the pk4 files and play the game that way... but it would be messy on your computer and it would take up alot more drive space because pk4 files are compressed.

- you can put everything except the the description.txt file for your mod into a pk4. Or, you can put nothing into it. However, for your mod to work, you must have a pk4 file in the folder... empty or not.

hope that helps.