A rinse out is a conditioning tool. It does different things for different folks (detangle, smooth, prep for leave in or styler etc). It's the next step after cleansing, mainly used to moisturize. But mostly it does exactly what it says, which is rinse completely out of your hair. Some folks don't rinse, but at that point, it would be considered a "leave in"...
3B, Fine, Normal P, Normal E, Low-Med D
LowP: Kinky Curly Come Clean (50% EVOO)
NoP: As I Am CC
RO: Suave Coconut, VO5 Shea Cashmere
LI: KCKT or CJBCLI or HETT/HENOYF (w/ 8 drops GSO)

"To much is given, much is expected"