File types : depends primarily on end usage for print the range is 240-300 dpi, or for digital 72-92 dpi. Usually for digital web/mobile usage standard formats are PNG or JPG
File format of RAW vs JPG : maybe for a later lesson but camera Raw is always the best format to shoot in it gives you greater control of size and image manipulation
Layers : tutorial that gives an overview of Photoshop layers
Keyboard shortcuts : a good idea to learn some keyboard shortcuts, it cuts down radically on mouse fatigue
Adjustment Layers : tutorial here
Text and Retouch tutorial : this is a good one to go through just to have a sense of things
Tutorials galore : here and here