Custom fields allow you to have content included in your posts automatically changed based on the information saved against a service.
For more information on getting started with Custom Fields, please see this page:
So for example, if you were bulk importing posts that needed to go out to multiple channels but wanted to have a different URL in the post on each channel, rather than creating each post individually, you can create a custom field for that URL and then add the related URL under the 'Tags' section for each channel.
You'll then need to get the place holder for that custom field which you can do by opening the Compose Box and then:
1. Select the content icon.
2. Select Placeholders.
3. Then Channel Tags.
4. Then select the checkbox next to the custom tag placeholder before clicking the Insert Selected button.
5. You'll see that the placeholder is added to the Compose box with a specific ID number, copy this and place it into the Message field when bulk importing either in the bulk importing view or if you're importing a CSV file.
The system will then automatically replace the placeholder with the URL that you've set up under the Tags option for that service/s.
For more information on bulk importing, see: