If you are using .023-.025" bare wire with argon/co2 gas mix, your wire feed range is 100-400 inches per minute.
100 being for the thinnest steel you can weld,
400 ipm would be used for the absolute thickest steel the machine would handle.
Voltage is another story. I say set the wire feed speed first. then get a piece of scrap metal the same thickness you want to weld and adjust the voltage until you get a nice bacon frying sound.
Too little voltage and it will snub and sound like a drive by shooting.
Too much voltage and the wire will try to burn back into a ball or the sound will be a rattle or hiss.
You will see....its very hard to describe but just try it.
so if you wanted to weld 20 ga. or about .030" thick. you would set the wire feed speed to 100. if it does not read in inches, just pull the trigger and count to 6 seconds, measure in inches and add a Zero.