It may already be enabled, you need to enable it on your mobile phone to see if it detects it and input any security code when prompted.
You will need the software for your mobile phone installed on the pc. If you have a Nokia, you can dowload the Nokia suite for free from their website. Likewise Sony Erickson, Samsung you may have the disk supplied with it. Others you will need to check their websites.
In any case read the instructions for your phone on how to connect.