If you already have a website and a domain how do you publish it?

Presumably you have built the website on something like Microsoft Publisher or Power Point. You will need to "publish to the web" which will convert the files to web format.

Download Filezilla (free download). Use it like Windows file manager. You will need hosting, available from the place where you purchased the domain. Enter your domain into Filezilla where there is a blank for host. Enter your passWord. Then just drag the website files to correct folder on the host.