pico_led
sets up pin 25(the led) to blink

  gpio_init(25);// init pin 25(the led)
gpio_set_dir(25, GPIO_OUT);//set pin 25 to output

Turn On LED

  gpio_put(25, 1); // Set pin 25 to high

Turn Off LED

  gpio_put(25, 0); // Set pin 25 to low.

wait for 250 ms

  sleep_ms(250);

Code: 

  #include <iostream>
#include <stdio.h>
#include "pico/stdlib.h" // the pico-sdk lib


int main(int argc, char const *argv[])
{
    stdio_init_all();// allows printing to terminal

    gpio_init(25);// init pin 25(the led)
    gpio_set_dir(25, GPIO_OUT);//set pin 25 to output

    while (1)
    {
        // Turn On LED
        gpio_put(25, 1); // Set pin 25 to high
        sleep_ms(250);//wait for 250 ms
        printf("LED switched on!\n");// print 
        // Turn Off LED
        gpio_put(25, 0); // Set pin 25 to low.
        sleep_ms(250);
        printf("LED switched off!\n");

    }
}