[GregH]

There appear to be several different models that sport the Flux Core 80 name.
Some are listed as Mig/Flux Core 80 which come with the gas regulator and electrical connections in the machine to make gas welding happen.
The instructions for yours should tell you what you have.

My personal opinion is that a welder like this is a purchase that should last many years and I do not feel these homeowner units are a good investment because of their quality and availability of replacement parts.
Also, the maximum amperage and duty cycle of a machine that is suppose to operate on a 15 amp 120 volt receptacle would make it too frustrating to weld anything much more than sheet metal.

And yes, sheet metal is better welded with gas as it tends to cool the material and allows slightly more current without burning through.
You might want to try a start and stop or stitch technique to allow a bit more heat in one spot.