Yes you can use it in the power steering, but only a little.
I the engine oil, that little bottle should be way less than a pint, so, no, you don't have to drain any oil. Having said that, it works best on fresh oil.
The Archie certainly quieted down my engine when starting during the winter, I put it in when I change the oil in the fall.
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.