Secondary WordPress domain?

I bought my organization’s domain (www.millennialaction.org) from GoDaddy and purchased a WordPress package through GoDaddy. In my settings, it says my WordPress URL and Site Address URL are both the same (millennialaction.org). However, my past experiences with WordPress have been where WordPress gives you an automatic “username.wordpress.com” URL before you purchase a custom domain.

My question is: Does that WordPress-branded URL exist for my website as a secondary domain?

I are going to be pointing this domain from WordPress to Squarespace soon, and am wondering if my wordpress site will live at another domain afterwards or will just vanish and be inaccessible from Google.

Thanks.