Complex sentence: They have a prehensile tail with which they often use to grasp objects and/or hang from them and will often curl up in a spiral pattern while idle, and unravel for balance while walking.
Split into simpler sentences: They have a prehensile tail with which they often use to grasp objects and/or hang from them. While idle, the tail will curl up in a spiral pattern and unravel for balance while walking.