读手册就好了，不难
r_task_priority.h

#define TASK_BLINK_TASK_PRI			(5)

main.h

int_t os_blink_task_t(void);

main.c

int_t os_blink_task_t(void)
{
    /* never exits */
    while (1)
    {
    	printf("hello world\r\n" );

        R_OS_TaskSleep(500);
    }

    return (0);
}