Yes, KL25P80M48SF0RM.pdf. Read as much of it as you can. The only way to really learn an MCU is to read the manual.
See also DDI0484B_cortex_m0p_r0p0_trm.pdf, DDI0419C_arm_architecture_v6m_reference_manual.pdf, Cortex-M0_Plus_Intro.pdf.
If none of that makes sense, then you need to learn intro mcu stuff, and this is probably not the best choice for your first MCU, if for no other reason is is pretty new.