This can be done by visiting Steams API page
Once there you'll be asked to enter a "Domain Name", Anyname will do. I personally chose my Steam username. Agree to the terms and click "Register". You should now see your API key listed there(Valve recommends you keep this key private). Copy and paste your key into a text document for now.
The next step is to head over to the Steam Workshop and select your game of choice. Click on "Collections" from the top menu, then in the right hand menu click on "Create Collection". Fill in all of the required information and describe what type of collection you'll be making. Once that is done scroll down to the bottom and press "Save and continue". The next screen allows you to add items to your collection in three different categories. Things you've published to the workshop, favorited items and subscribed items. Obviously, you'll need to have the things you want added to your server either subscribed to or favorited already. Once you've added everything you want to add click "Save and Continue" at the bottom. On the next page you can add a background image for your collection or simply press "Publish".
Your collection is now published and you are ready to get its collection ID. Look at the end of the address bar for "id=". It should look something like this.
Code: Select all
http://steamcommunity.com/sharedfiles/filedetails/?id=147099037
Scroll down to the bottom of the page and click on "Commit changes". Restart your server and it will automatically start downloading your collection.
P.S While the Steam Workshop is normally pretty fast, depending on the size of your collection it can take upwards of 30 minutes to download everything. Until the download is complete your server will be in a frozen state once started.
Update
With the newest patch, it is also necessary to create a resource file to force the clients to download your collection if you're using Garrysmod. We have a guide on how to do this here:
How do I force content to be downloaded?