how to blink an LED

First, see "why blink an LED?"

There are lots of ways to blink LEDs ranging from learn-the-hard-way to trivially-easy to massive-overkill. Here are a few ways relevant to this project.

If blinking an LED is all you want to do, then just let the RTOS do all the work for you:

examples/blinky built into RIOT OS

But of course you're going to want to do a lot more than just blink an LED, so use the fargin framework:

blinky.minimal partial (minimal) framework

blinky.serial-service access primitives on the target from a PC

blinky.satellite-service blink an LED no matter where on the planet it is located