problems hooking up propane tank to grill
It does appear that this grill is made for, or has been converted to use natural gas rather than propane.  To convert a grill, you need two things - a new hose/regulator assembly and new gas orifices for each valve/burner.

The hose and regulator needed for a propane grill are pretty universal and easy to find.  The problem is the orifices.  This is a part that has a tiny hole in it inside the valve that allows the exact amount of gas to come out.  The orifice for natural gas is larger than propane so using the wrong orifice could result in a dangerous situation (overheating/fire).

You will need to contact the manufacturer with your grill model number to see if a conversion kit is available.  This is hit or miss - some grills have them and others don't.  I've seen super cheap grills that have kits available and very expensive ones that do not.  There is no "universal" orifice kit.

Do not attempt to run the grill on propane without the proper conversion kit.