getting acquainted with Photoshop

I am a new guy at Photoshop exercises.
I found a tutorial on the web and step by step I teach to work with this program.
It is quite difficult to remember all the peculiarities but I believe practice makes perfect and I will be able to make the complicated things (complicated in my vision) with no prompting of the tutorial. Here are some of my works:
The easiest exercise: to make colored pieces of a gray scaled picture:


Here are my attempts to make an explosion, I did not catch the idea of the tutorial, but I do like what I made:
I also tried to make a spiky balls, I think I succeeded in it :)

Another point is creation of a simple three-dimensional ball, I saved it already but thought that without shadow it look a bit strange. Well, I am working on the issue :)

Here is my try to make a pictures with replaced colors of certain parts. The original flower was yellow.

Have you ever tried to make water of nothing? Here is what I managed to do:

Here is my second work in this field:

I suppose this one is more successful.
Any comments on the topic?
Most welcome