Basically, the cable directly connects the supported Apple device of choice with the bass or guitar. Audio can also be diverted to either headphones or an amplifier.
The iRig is meant to be paired with one of the three apps specifically developed for this accessory, all of which are available for download from iTunes. Ranging from free to €15.99 ($), the app will include a various number of stompboxes, amps and microphones for mixing your music. You can get the gist of it by taking a glance at the images of the potential options.
Developed by IK Multimedia, the iRig is only compatible with the iPhone 3G/3GS/4, iPod touch 2nd and 3rd generations, and the iPad. The iRig itself is $39.99 or €29.99, depending upon which side of the Atlantic you reside.