Install Cubase and test it is working. Install any drivers for your audio interface if necessary. Install Guitar Rig and ensure that the "Guitar Rig.dll" file appears in the "C:\Program Files\Steinberg\VstPlugins" folder. Connect the audio interface to the USB or Firewire port. Launch Cubase and create a new project. Click the plus sign at the top of the Arrange window and create a new stereo audio track.
Connect the guitar to the audio interface using the 1/4-inch lead. If your interface has more than one audio input, use Input 1. Select "Mixer 2" from the Window menu in Cubase, and locate the mixer channel for Input 1. It will most likely be the first channel on the far left of the mixer. Click the button with the lowercase "E" symbol, and select Guitar Rig from the drop-down menu. Return to the Arrange window and select the audio track.
Click the button with the speaker symbol, and turn up the volume on your guitar. You should be able to hear the Guitar Rig effects. To edit the effects settings, return to the Mixer 2 window and double-click the Guitar Rig button on the input channel.
This process allows you to play through Guitar Rig in real time, like an effects unit.
Click the plus symbol to create a second audio track. View the track in the Arrange window, and click the drop-down box under the track name. Select "Guitar Rig." Ensure that the speaker button is deselected. This configuration will allow you to apply Guitar Rig effects to audio files you have already recorded. Drop a guitar part or bass line onto the track, and double-click the "Guitar Rig" button under the track name to edit the settings.