if you don't use SDK, you can take a look at this set of examples:
https://www.nxp.com/docs/en/application-note/AN5413.pdf
https://www.nxp.com/webapp/Download?colCode=AN5413SW&docLang=en
If you use SDK, you can take a look at examples in SDK like:
c:\NXP\S32DS.3.4\S32DS\software\S32SDK_S32K1XX_RTM_4.0.3\examples\S32K144\demo_apps\hello_world\
Or any other which uses GPIO...
The documentation can be found here:
c:\NXP\S32DS.3.4\S32DS\software\S32SDK_S32K1XX_RTM_4.0.3\doc\S32SDK_S32K144_UserManual.pdf
If you are not familiar with SDK, you can take a look at quick start guide:
c:\NXP\S32DS.3.4\S32DS\software\S32SDK_S32K1XX_RTM_4.0.3\doc\S32SDKQSG.pdf
Regards,
Lukas