The process is as follows.
You register your domain abcd.com with the domain registrars like godaddy.com / register.com ........
Now majority of the domain registrar also provide the hosting and so you have 2 options.
1. Buy hosting from them and they will automatically integrate your website and will give you FTP access where you can do all the hosting and managing related work.
2. You choose some one else for you hosting and then your hosting provider will give you name servers which you need to update with your domain registrar.
I hope that helps.