'Audio Cutter' is the easiest-to-use Audio Cutter App on the App Store.

Just browse your audio file from your MAC or PC via USB Cable from iTunes, or get your audio file opened from other Apps, then move with your fingers to cut your audio file while listening to the trimmed part, and then finally tap on export to save your trimmed audio file to your iTunes Shared folder to be transferred to your MAC or PC via USB Cable to iTunes, or send your trimmed audio file as an attachment in an e-mail, or open-in it in other Apps.