To create parts in Revit architecture, you have to
Go to the contextual ribbon
For example, you select a basic wall with several layers
When you select on create parts, each layer of the wall will start behaving as a separate layer
After creating parts, you can further divide them by selecting the option divide parts. While
doing so you, have to ensure that you are not selecting the original element but the part itself
After that you will see that your part is divided into smaller parts
