But when I tried to purchase a hosting plan on Godaddy, it asks for the domain name for which I want to host. And when I add, healthcurings.com, it says, the domain is already taken.
That's not a WordPress.ORG problem but I'll explain.
Your domain is hosted on WordPress.COM and you need to speak with them to get the domain hosted on GoDaddy. That is not something we can assist you with.
You're also posting in the wrong place and need to ask in the correct forum.
http://en.forums.wordpress.com/forum/support
This forum here is for self-hosted WordPress.ORG software installations. You do not have one yet and if you post to that other forum I am sure someone can explain what steps you need to take to migrate to GoDaddy.