Call function whenever somebody makes a post?

Hello, I am curious if there's a good way to call a custom function when somebody makes a post. I'm using a Steam integration plugin on my website and would like to be able to access my gameserver databases to reflect on users in-game credits whenever they make new posts.

Handling the database outside XenForo I am capable of coding, though I don't know how I could grab the user's steam id (entered by a custom field included by the plugin above), and call a function when a new post is made.

edit: Did some reading (which should have been done before-hand), and discovered what I needed to know!
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