I am trying to make a basic forum/board where anyone can simply post a message via a submit for. So far I've been able to send the text they've entered via POST and put it into a MySql table. I am wondering how I then can go and print on the webpage what was just submitted?
Well if it's on the same page / script as the MySQL insertion, then you can take it from post, however I suggest using htmlspecialchars() to remove any HTML that people could embed in to their data.
If it's not on the same page, as it won't always be, then use MySQL to retrieve the data with a SELECT query - See here for help: W3Schools - SELECT - and, again, use htmlspecialchars() on it and display it in your desired format.
This is a very vague question for StackOverflow, so I can't really give you much more information unless you give me something that you've already tried, something I can correct / alter.