Hello there, welcome to Pixelation, hope you enjoy your visit here and I'm hoping I can help you out in one way or another, you seem to be new at not only pixel art but the art field in general, so bare with me while I critique your piece.
Alright, it doesn't seem like you've used any reference, if you don't know how something looks, remember: its okay to look up reference
.Another thing I want to note is that make sure you define your light source and I'm not sure what else to say on the subject, I hope the edit speaks for itself.
As for your photoshop problem, change it to the pencil icon by right-clicking on the brush and go to eraser and change it to block, this way you can work with pixel pieces on photoshop, though I think theres much more you should do before that, I have some suggestions for you, links follow:Andrew Loomis Books
Andrew Loomis' "Fun With A Pencil" is what I suggest you download first, his books are great for beginners.*A lot of useful links and tips on art
Lots of links on where to get more tutorials, reference, basically anything art-related.So You Want To Be A Pixel Artist?
This will help you get started on pixel art, this guys very good at pixel pushing and his tutorial is great, I used it too when I was starting out.Ten Minute Drawing Techniques
A lot of good art tutorials on youtube.
Alright man, I hope I've helped you, enjoy your stay here and have fun pixel pushing!
*I'm not sure if I'm allowed to put thise link up, they're just e-books but yeah.