Action Details
Requirements and how-to articles for Steam's action:

Every product on Steam has its own unique hub. By default, your community hub will be set live as soon as your product's release state is set to 'Coming Soon'. Users can post content here such as artwork, guides, discussions and videos, but you can also upload this type of content to your hub if it is feeling empty.

You need this to get it done:

You can promote trusted community members or add internal team members to help moderate your Steam Community Hub. (See official documentation for more details.)
Artwork Title
Give your artwork a title (maximum of 128 characters.)
Artwork Image
File format: .jpg/.png/.gif
Maximum file size: 8MB
Artwork Description
Use this space to describe your artwork or what was involved in making it (BBCode formatting available, maximum of 8000 characters.)
Guide Title
Enter the title for your guide (maximum of 128 characters.)
Guide Branding Image
This image will represent your guide in the Steam Community. When users search, browse, or filter the list of guides this is the image that will appear next to your guide. For best results, use something that represents the theme or contents of the guide.
Aspect ratio: Square
Dimensions: Minimum of 195 x 195 pixels
Guide Description
Use this space to describe your guide, what makes it interesting, and what the scope is. This will appear as the description when browsing through the list of guides for this game. (BBCode formatting available, maximum of 8000 characters.)
Guide Categories
Choose which categories your guide belongs in (e.g. Achievements, Gameplay Basics, Secrets) and the language it is written in.
Guide Contents
The contents of your guide are split into separate sections, which will be listed in the table of contents when your guide is published. Each section has its own title and a maximum length of 8000 characters, with BBCode formatting available. You can also add images, screenshots and videos.
Guide Images
Select and upload images you wish to reference in your guide (upload all the necessary images and they will be easily selectable when editing individual sections of your guide.) You can select multiple files to upload at once, but only up to 8 MB at once.
File format: .jpg/.gif/.png
Discussion Title
The title of your discussion.
Discussion Content
The content of your discussion. (BBCode formatting available.)
Discussion Category
Choose the sub forum to post your discussion in (e.g. General Discussions/Events & Announcements/Help & Support.)
YouTube Video
Videos must be uploaded to YouTube before you'll be able to submit them to the Steam community. YouTube videos must be set to public and embedding must be enabled, and your Steam account must be linked to your YouTube account.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

Steamworks Documentation - Steam Community
Information about Steam Community Hubs and Discussions.
Steamworks Documentation - Community Moderation
Information about moderation tools, warnings, bans and messaging.
Link missing here or found errors? Improve How-Tos