Construct 2 manual ?
Edit: Also the usage of photoshop has little to see with "Game making".
It's a tool to perform some operations/ressources on the path of game making.
Photoshop is not the only tool available (gimp, paint.net, sai, graphicgale deluxe, etc...) and being a complete software with its vocabulary, workflow, tips and habits, etc... once again it goes far beyond the scope of this forum.
There are already tons of documentation (and in multi-languages as opposed to scirra being english only at the moment) nothing that could be written on scirra on that subject could surpass what's already out there.
Searching for documentation is one of the skills required in game making, practicing is the best way to train it.
The internet is wide, don't be scared to explore it, most of the time it doesn't bite.
If you're just coming to this one site waiting to be spoon-fed informations, you're already doing it wrong.