Why don't I have a custom title by now?!
You should have the following files in the same folder:
i tried dragging and droppin already. am i supposed to have everything in a specific folder?
Those are the bare minimum. Note that Windows, by default, hides file extensions, so you might just see "zdoom", "zdoom.pk3", and "fmodex". It might be a good idea to show file extensions first. Here is how you can do it on Windows 7, Windows Vista, and Windows XP.
- zdoom.exe (or gzdoom.exe)
- zdoom.pk3 (or gzdoom.pk3)
These three files are the bare minimum and they should be together.
Now you need IWADs. If you have bought The Ultimate Doom or Doom II on Steam, make sure they actually are downloaded on your computer. ZDoom will find them automatically.
If you did not get these games from Steam, you need to retrieve the IWADs. For The Ultimate Doom it is doom.wad; and for Doom II it is doom2.wad. There are also other IWADs you can use, see Doom Wiki or ZDoom Wiki for further information.
If you do not see a doom.wad or doom2.wad file in the folder where you have placed your Doom games, make sure the game is properly installed. You might need to run install.exe in DOSBox. If that seems too complicated, download Freedoom.
You should then have zdoom.exe, zdoom.pk3, fmodex.dll, and doom2.wad, all in the same directory. Double-click on zdoom.exe: the game should start. It will create a zdoom-<username>.ini file in the same folder, where the game will store the changes you make to the configuration (for example, if you change the key bindings). Once you have that file, you can edit it to change the paths in which the IWADs are sought, so you no longer need to have the IWADs in the same folder if so you want.
If the game started correctly, you can try the next test. Choose a mod you want to play, verify it is for the same IWAD (don't try a Heretic, Hexen, Ultimate Doom, Strife, etc. mod for Doom II), and drag-and-drop that file onto zdoom.exe. The game should start with the mod.