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

Requirements
You need this to get it done:

Chosen Curators
You can use the controls to filter the list of Steam Curators to pick from. You'll want to identify Curators that have an audience that is likely to be interested in your particular game.
You can send offers to 100 Curators, with a maximum of 5 copies of your game each.
(Note: Your game needs to have at least a 'coming soon' page publicly visible before you can send copies of your game to Steam Curators.)
Message
You'll also need to include a message to the Curators. This should be brief. Along with the message, we automatically include information about your game such as name, logo, screenshots, and primary tags. In your message, you want to get to the point and tell the Curator why their audience will care and what is special about your game. If you wish for the Curator to contact you for more information, please include your contact information as well.
Game/Application
By default, the package that is sent to Curators is created with the same contents as the base store package for your game. If you add new depots (such as new operating systems), you'll want to make sure you add those to your Curator package as well. You can also add more content to this package if you wish to also send DLC or soundtracks or other additional depots to Curators.
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How-To Articles
A list of useful links for you:

0
Steamworks Documentation - Curators and Curator Connect
Information about Curators and and how developers can make use of Curator Connect.
Official
Link missing here or found errors? Improve How-Tos