photoshop reflection

Before today, I never used photo shop. All that I really knew about photo shop was that you take out things and touch up pictures.  All i ever saw that involved photo shop was a video on instagram of someone changing Kendall Jenner into a pizza slice.  I had diffuculty finding out different techinques i could use. I needed up asking my peers and digging into the worksheet to help out.  I didn't use a lot but my question would be '' How do you undo something?" i made lots of mistakes but i simply just uploaded my picture again and again.