Step simulates a physical world. The main part of Step (1) is the world scene in the center of Step main window where you first place physical objects and where you see the simulation. On the left of this scene a palette (2) let you choose your physical objects. You can freely move this palette anywhere on your desktop by dragging the title bar. On the right of the scene you can see the current world description (3), its properties (4), some help to explain some words (5) and the history of the current world (6). Each of those panels can be placed elsewhere on your screen by dragging the title bar.
To help you get started, Step integrates a series of tutorials which easily teach you how to build an experiment. Please see step by step to start with the first tutorial.