"PSD to HTML" is a workflow, here a web page is designed in a Photoshop Document (PSD) and then converted to code (using HTML, CSS, and JavaScript).
It would be difficult to start coding if you don't have an idea about what the final result is going to look like, so design the layout in Photoshop first and then create HTML of it.
We're capable of converting any type of PSD design to responsive HTML without breaking or changing it's design.