When creating a mod, be it a simple add-on or a fully fledged total conversion, you need to set an entry file so that it can be listed by the Mod Launcher or just started by the game.

This means that you need to create an XML file with name entry.hpc in the root directory for your mod, and its contents will depend on what kind of mod you are creating.

Any valid entry.hpc file will have at least the following attributes:

<?xml version="1.0" encoding="UTF-8"?>
<Content Version="1.0" 
    Type="" 
    Title="" 
    Author=""	
    Description=""
/>

• Version: The version for the entry file. Since new features might be added in the future, this attribute must be set according to the rest of attributes.
• Type: (String) The type for the content the mod is offering. Possible values as of version 1.0 are “AddOn” or “StandAlone”.
• Title: (String) This sets the title for the mod. Should not be longer than 128 characters, especially if the mod is to be uploaded to Steam Workshop.
• Author: (String) This will be shown below the title on the info column in the ModLauncher app.
• Description: (String) A brief description of what the mod is about. Should not exceed 8000 characters for the same reason as title.

Keep on reading for specifics on each Mod type:

This page explains the specifics for setting up entry.hpc files for add-on mod type.

• LanguageFolder: (String) This tells the game where to look for additional language files when the add-on is launched. Should be a path relative to the mod root directory. This value is optional, if your add-on does not add any language entries, then there's no need to have it.

A sample mod for a minimal add-on entry can be downloaded here.

This page explains the specifics for setting up entry.hpc files for Stand-alone mod type.

• LauncherPic: (String) Points to an image file that will be displayed on the details column in the ModLauncher app. Should be a path relative to the mod root directory.
• InitCfg: (String) Points to a configuration XML file that will set a list of initialization values including save directory, script modules config, and so on. Should be a path relative to the mod root directory.

A sample stand-alone mod for a minimal custom map entry can be downloaded here.