It's an $89 welder. Of course it's a cheap import from Asia.

On the machine you choose which input you are using. It all depends on how you choose. Is it a switch? Or is it determined by how you wire it.

Does it come with instructions?

No instructions in regards to power plug. The voltage switch has a locking mechanism. Not just flipping switch to adjust.

I believe that I could test to determine the hookup, if necessary. But first I would google.the brand and model number to see if anything shows up. No doubt others have encountered the same situation. From the little I know about color coding outside the USA, the Brown is one of the non-grounded conductors. So do a continuity test with that and with the others. The equipment grounding conductor should show continuity to the housing of the welder - and to nothing else.
Some of those welders are satisfactory and others are --. I am spoiled on a Lincoln high amperage DC with high duty cycle.