To get the most out of your Garmin cycling computer, you will want to add some accessories to capture more data. The most popular ones are speed sensors (http://amzn.to/2hLoWuC), cadence sensors (http://amzn.to/2iHm56z), and heart rate monitors. In videos shown here, I pair my sensors to a Garmin Edge 520 cycling computer (http://amzn.to/2iI7PKO).
First things first, you will want to install your sensors. Below are instructional videos for installing and testing speed and cadence sensors.
Now that your sensors are installed, you are ready to pair them with your device. Here is a video showing this process for the Garmin Edge 520:
With these accessories successfully installed and paired with your computer, you are ready to ride! If you have any questions about this process or gear, please leave a comment on any of the videos on YouTube and I will do my best to help out.