Download MPLAB IDE 8.92 which is the latest version.
The Simulator comes with the IDE.
You do not need anything to do with MPLAB X. Stay away from it.
The example programs should show you how to use the functions.
Use the menu options 'Project/Open' to run the examples.
There is a pdf document in the doc folder that details the implementation.
It is a basic RTOS, but that makes it very easy to use, very small footprint and very fast context switching.
Let me know if you have any problems and how you get on.