It is pretty much the same as TIG welding. You have to use a rod that's suitable for the material being welded, of course. The most commonly sold rod for mild steel is RG45, any welding supply should have it. You could use the rods you use for TIG, or a length of MIG hard wire, or even a coathanger, though the latter isn't recommended for critical welds. No flux is needed for welding mild steel, the properly adjusted neutral torch flame produces an adequately inert exhaust to act as a gas shield.
The big trick to gas welding is to get the flame adjusted properly. You want a neutral flame, an oxidizing flame is very bad, and a carburizing flame is generally too soft. The way I adjust for a neutral flame is to start with a carburizing (soft) flame and add oxygen until the outer cone just merges with the inner cone. This is obvious when you try it. Of course you also need to set your regulator pressures to values suitable for the tip size chosen (and tip size is determined by how much heat you need to do the weld). The booklet which came with your torch should have a chart. If it doesn't, there are charts on many of the websites of welding suppliers.
One difference with TIG is that you don't have a pedal. You control the heat by manipulating the torch position relative to the work. You get the most heat when the tip of the inner cone is *just* shy of touching the work. Back off more to lower the heat to the joint. If you have to back off more than about 1/4 inch, you're using too large a tip for that welding job. Movements while welding are otherwise pretty much the same as for TIG.
Gary