No clue how to get past it, couldn't find any information online.

All I've gathered is that I have to make Vitriol, which I understand is made from Lava and Energy in the Essence Purifier, but I have no clue how to do this.

I can't even put lave into my EP at all, I see that there is an upgrade costing "40 essence" allowing it to extract essence from one more type of raw resource, but I have no clue how to get this 40 essence. 

I don't have any way to transmute or anything, very stuck :(

Have you clicked the info button on a machine?

It tells you which element goes in which input.

Also transmuting appears sometime when you get essence.

Yes. I've checked, double checked, and triple checked each machine's output and inputs. I just figure I was on an old version or something and it was bugged.

try everything in the essence purifier 

You get essence itself by distilling the essence of power. Use essence to power up the machine, then you can extract it from lava to get vitriol. Check which inputs are allowed on each machine and you'll have a pretty good guess at what goes where