Hi Michael,
The MCUXpresso SDK has a standard API for the NXP MCUs. Several API functions may differ because of driver deltas across several MCU families.
To help you further to get started, it may help the following:
Check the MCUXpresso SDK API Reference Manual for the MKL25Z4 to get an overview of the available API functions of the FRDM-KL25Z SDK, here are some options to do this:
1 https://mcuxpresso.nxp.com/api_doc/dev/1364/index.html
2 Download the API reference manual after build an SDK from MCUXpresso SDK builder.
3 A cool feature of MCUXpresso IDE is that lets you open SDK documentation from a previously installed SDK.

You can also check the MCUXpresso config tools, it enables you to configure with ease peripherals, pins and clocks using a graphical interface.
Here, is a neat training series.
Basic Application Development Using MCUXpresso IDE and MCUXpresso Config Tools
Another advise is to take a look at the Erich Styger blog MCU on eclipse https://mcuoneclipse.com/
He has useful tutorials for the FRDM boards ( including KL25Z) .
There are a lot of ways to get started, and they depend on what do you want to achieve, in this community we have several document and posts that may help you. I also recomend you to take a look at our application notes for the KL25 or Kinetis MCus.
I hope this helps,
BR,
Diego