I am coming from a web design / development background and I'd like to study mobile app user interface design. For websites, I'd usually create a mock-up on Photoshop (or other photo / design editing tools) and then convert my design into HTML / CSS before adding in any functionalities (using PHP / Javascript).
However, when it comes to designing iOS apps, how do I convert my Photoshop / Sketch designs into an actual iOS user-interface? Do I need to study a new mark-up language (similar to HTML)? Or is it going to be a drag & drop interface (similar to Flash) wherein I only have to worry about coding the functionalities / interactions and not coding the actual interface design pixel by pixel?