Sketch uses one unit, styles only relevant to UI design, a built-in iPhone previewing tool called Mirror and Artboards, the most efficient way to template multiple screens.
Design isn’t hard to learn. That’s because most of us are already building products and are familiar with what design means. What used to be complex and confusing is now simple and effective, thanks to Sketch, an app that is entirely focused on user interface design. Unlike Photoshop, you don’t need to worry about photo editing and the hundreds of other settings that are noises to designing a simple application.