Steroids CLI allows you to run your application in a simulated/emulated device on your computer. Depending on the platform there are a couple of options. iOS applications can be simulated with the simulator that comes bundled with XCode. This requires you to run Steroids on Mac OS X. See iOS Simulator.
For Android applications, Steroids CLI ships with support for two different emulators. Android Emulator that comes bundled with Android SDK and Genymotion. We strongly advice using Genymotion. Note Android emulator support is work in progress and only tested on OS X.