How

How does a user know where they can and where they can't post

It looks like you are in Oklahoma so this thread http://www.eccie.net/showthread.php?t=19329 is very detailed on the advertising guidelines. The same thread is stuck at the top of every single Provider Ads forum in every city/state forum across the entire site.

There is a second one stuck right beneath it that explains what you need to do to get Verified Provider status with us. Once you have that, then you can begin posting regular ads here.
For Oklahoma, this thread http://www.eccie.net/showthread.php?t=455458

To carry that further, each are also has a Welcome and Introductions forum. If you look at the header of that forum, it also explains it

Welcome and Introductions - Oklahoma This local-based forum has been designated as a place to introduce yourself to the community, and to welcome new members, both male and female. Feel free to let us know about yourself here. (New Ladies: You may post your info here during your first week of membership, but please contact the local staff to request Verified Provider status. Once verified, you will be enabled to post in the proper advertising forums, build your Showcase, and access the ladies-only areas of the board)

Now, as a member here you are allowed join any discussion, almost anywhere on the board...as long as you are not placing an ad, ads are limited to the proper ad forums (Provider Ads, Weekend Lineup and Welcome and Introductions of your local area). Joining some of the general discussions is a great way for folks to get to know you and your personality a little bit.