Learning New Photoshop Tricks

I'm taking a free mini class on campus on photoshop,
and learning to manipulate layers and masks.
I have always avoided this before
(it seemed too headache-inducing)
but I think I am going to want to learn to play with this.
Observe my rose, for example.
(The original photo is not mine,
though I've photographed similar settings.)
This was an exercise in mask making and selecting,
so that we could make a black and white background
but with selected color bits.
I expect this could be quite fun to twiddle with.
I have a HUGE stock of flower photos...