How do you go from website design in Photoshop to a functioning HTML & CSS website?

Zack,

Different people will have their own methods to go from a PSD to a live, working site, and nowadays, there are plenty of alternative methods to get you from conceptual designs to the finished product, as well. Depending on your timeline, budget, preferences, abilities, and requirements, you may be able to bypass Photoshop altogether, should you desire. Photoshop can be a useful tool for putting together high-fidelity mock-ups, but if you're not very familiar with it and don't have the time to learn it, it can be quite time consuming and difficult. As an alternative, you can design with bare-bones wireframes for structure and layout and style guides for aesthetics (color palette, button styles, etc.), or you can put together minimally interactive prototype pages with some quick coding to send to the client for notes and/or approval, which is an especially attractive method these days even if you aren't the fastest on your own with HTML/CSS, thanks to frameworks like Foundation and Bootstrap (and, as an added bonus, Treehouse has courses that introduce prototyping in both of those frameworks, like this one). Either way, it's even easier to really fine tune and design in-browser with wonderful things like Chrome's Dev Tools.

If you are working from a PSD, though, you'll build the site out in much the same way that you would with any other process. Typically, when I am working from a PSD, I use it to get exact dimensions for certain things that I know my designer has put in there (such as the maximum outer and inner widths of the site as a whole), but other than that, you still break it down as usual: I build out the header first, then the footer, as those will be common across all the pages, then work on whatever other repeatable sections you might have (such as hero images on pages, or common sidebars, etc.), then get to the page specific sections, layouts, and styles as necessary.

Ultimately, how you build your site will depend on the things I mentioned above (timeline, budget, preferences, abilities, requirements), but there isn't necessarily a right or wrong way. PSD to HTML is becoming less and less common, though, and in fact, Treehouse's own Nick Pettit wrote a blog post on the topic last year that you might be interested to check out!

Erik