Drawing in photoshop can be difficult if you haven't used it for drawing before. it takes a bit of time to get used to the tools and masks. What I would suggest is going on youtube.com and searching for "Manga Tutorial Photoshop". There will be some useful video's. Video's are always easier when you can actually watch what someone is doing instead of just reading instructions.
To be honest, when I draw in photoshop what I do is draw my picture on normal paper, Scan it onto the computer, and paint it and draw it in photoshop with a tablet. it's easier then starting from scratch in photoshop.
Have fun!!
