Complex sentence: Working memory is the system that actively holds multiple pieces of transitory information in the mind for execution of verbal and nonverbal tasks--such as reasoning and comprehension--and makes them available for further information-processing.
Split into simpler sentences: Working memory is the system that actively holds multiple pieces of transitory information in the mind, where they can be manipulated. This involves execution of verbal and nonverbal tasks--such as reasoning and comprehension--and makes them available for further information-processing.