Applications » Guide me to use Avast license key for activation

I am using paid version of Avast antivirus, so I am using Avast license key to activate this antivirus for a few years. But I don’t have knowledge to use this key in the proper ways. I am just new to this process. I am not perfect for activation procedure. So, I am looking for the best service provider and antivirus experts. So, please suggest me anyone, who is looking for the reliable ones.