I am good in almost full-stack of web development except design. Not the html,css stuff but the photoshop stuff. I want to close this gap, how do I get started?
Yeah, design is a separate discipline from programming and has to be considered on it's own. It can't be boiled down to just a set of techniques (Photoshop techniques, in this case). It's important to learn design theory (what you'll get from those Peepcode play-by-plays or from some good design books) and the practical techniques (what you'll get from sites like http://psd.tutsplus.com).
I'd recommend tackling both design theory and Photoshop techniques, unless your only interest is in implementing other people's design work and you just need to know Photoshop techniques to translate that work from PSD to HTML/CSS.
IMHO with CSS3 you can design a site that's nice enough in just HTML/CSS... if you're already a web developer I would spend your time designing in the actual HTML/CSS. Start trying to mimic good design elements. You probably won't get to the absolute top tier of design, but my assumption is you want to get to "good enough".
I recommend you to watch some play by play from peep code. Since I watched them I understood the process to design a good UI:
https://peepcode.com/products/ryan-singer-ux
https://peepcode.com/products/play-by-play-kneath