Guitarix takes the signal from your guitar as any real amp would do: as a mono-signal from your sound card.
The input is processed by a main amp and a rack-section. Both can be routed separately and deliver a processed stereo-signal via Jack.
You may fill the rack with effects from more than 25 built-in modules, including stuff from a simple noise gate to brain-slashing modulation f/x like flanger, phaser or auto-wah.