Hi sjftrver,
Congratulations on your new Big Country and welcome to the Heartland Owners Forum. You'll find there's lots of useful information here along with a bunch of friendly people who are quick to offer help.
I've had AT&T DSL at home in the past, and based on that experience, I would guess that the park may have an AT&T DSL connection to the office, which they then distribute to the RVs either through a conventional ethernet splitter or through WiFi. Most parks provide internet service through WiFi. The reason I'm pretty sure they're not just running a phone connection to your RV site that also carries DSL, is that for a DSL signal to do anything in your rig, you would still need to sign up with AT&T to get the correct modem, and to have the service "provisioned", turning it on for you. Even if you had the equipment and a home account, it would still need to be provisioned at the park location. Unless it were a semi-permanent location, this wouldn't make sense for either you or for AT&T.
I'd suggest starting by asking the office for more specific information on how to connect to their internet. If it's via WiFi, they'll give you instructions on how to sign on. If it's via an ethernet wire connection at the pedestal, you'll probably have to get an ethernet cable long enough to get to your computer or router and probably run it through a window. I don't think any of our coaches are pre-wired with ethernet connections.
If you're looking for the telephone connection, it would be in the Universal Docking Center (UDC), if you have one. I think they may have been discontinued due to lack of interest in landline connections. Most people just use their cell phones or a variant like Verizon's Home Phone Connect device, which is what we use at home and take with us in the RV.