We get questions about this all the time. The site has a system to 'hold' questionable posts for review. The mod team gets a notification and reviews, then approves or disapproves posts.
This process generates a message automatically when the post is approved. New members often have this happen as they post links in threads or messages. Sometimes, when people don't see their post show up, they will re-post time and time again because they think something went wrong.
If you post and find out it hasn't shown up, wait a little while and refresh, then check again. Our approval queues get packed sometimes, but we will get to them.
Also, sometimes, you may get a message out of the blue that your post has been disapproved. This is a tool the Moderator team uses to put something on hold so it can be checked out. It may not even be your post itself that is a problem. Please be patient, as we will get back to you if a problem exists, or we'll Re-approve when we're done.
Thanks for reading and working with the system as it is designed!