Complex sentence: It is NETtalk's task to properly associate the correct pronunciation with a given sequence of letters based on the context in which the letters appear, ie. the letters around the currently pronounced word that provide cues as to its intended phonemic mapping.
Split into simpler sentences: It is NETtalk's task to learn proper associations between the correct pronunciation with a given sequence of letters based on the context in which the letters appear. In other words NETtalk learns to use the letters around the currently pronounced phoneme that provide cues as to its intended phonemic mapping.