Firstly, you may search this Forum, there are now more than a million messages,
many touching similar questions as yours.
As for PIC32 ... Oscillators and Clocking, the Harmony GUI Plugin application in MPLAB,
may be the most convinient tool to use.
In addition to Datasheet for the device you are using,
there is also a Family Reference Manual document for the Oscillator section.
The device on your board should be PIC32MX570F512L
Use the Product webpage for the microcontroller to pick up current revision of documents for the device:https://www.microchip.com...cts/en/PIC32MX570F512L
Harmony (MHC) is a code generator application,
so for simple peripherals and purposes, you may use the GUI plugin to select options,
then push a button and example code will appear.
The Datasheet will still be important, to understand what the various peripherals can do.
There is also Microchipdeveloper website with some tutorial stuff: https://microchipdeveloper.com/
Since you are familiar with 8-bit PIC microcontrollers,
You could also look at Microchip Code Configurator (MCC)
MCC will make code that correspond with register and field naming as described in the datasheet,
and may make code more similar to what you may be used to.
Note: use MCC plugin version v3.95.0 with Core v4.85.0 and device library for PIC32MX v1.35
It may also be possible to use plugin version 4.0. or later, with Core v4.85.0 and PIC32MX library v1.35
Core v5.0.1 or later will probably Not work with PIC32MX library v1.35