Hi Patricio
serial_port_uart.c defined LPUART APIs with user-defined settings, such as baudrate, parity mode.... please see functions Serial_UartInit/Read/write/...
These Serial_Uartxxx functions will call HAL_Uartxxxx, they are defined in LPUART_adapter.c
I would suggest refer to the uart demo for how to use lpuart driver .
SDK_2.6.0_EVK-MIMXRT1020\boards\evkmimxrt1020\driver_examples\lpuart
Please also read SDK API reference Manual: chapter 24 LPUART.
Regards
Daniel