I want to add a subdomain so that I can have a blog on my Shopify Store, that is on either Blogger or Wordpress. Which option should I choose to use a subdomain in this case?
I understand that part, I just don't know whether I'm picking option A or B afterwards? IP address or Alias?
You will need to create the site for the subdomain first either through Wordpress or Blogger and then add the subdomain to your GoDaddy domain's DNS. Check out this article on how to add the subdomain.