Adjustment layers

Hi, I am quite new to PS and I have been browsing internet for tutorials. I came across one that showed how to put two pictures - one on top of the other - and select "Auto Adjustment" whereby the two pictures become one and you can then erase parts of it - for instance if a person has their eyes closed in one picture you can erase it and it is aligned properly underneath. Hope you can understand what I mean. Anyway, finally the point I am making is that I cannot find the tutorial now - any help would be appreciated. Thank you.