At no point during the One Click install do you type your domain name.
If you select the Simple Install you supply a subdomain name. So if your domain is mydomain.com, you select it from the drop down list and type a name in the box to the left, example, wordpress. You will then have a web address of wordpress.mydomain.com to access WordPress
With the Custom install you select your domain name from the drop down then type a folder name, for example, Wordpress. You will then access Wordpress at www.mydomain.com/wordpress
Hope this helps