You would just need to point your purchased domain name to the UltimateWB nameservers which will be emailed to you after you have purchased the UltimateWB web hosting package and it is set up for you.
For a social media site, you are going with the UltimateWB Full version software? That will have the built-in social networking apps that you can customize. You can purchase the software at https://www.ultimatewb.com/buy . And for your convenience, here is the link to purchase the web hosting package: https://www.ultimatewb.com/domain-names-web-hosting . (These links are under the "Buy & Download" menu tab at the top.) All UltimateWB web hosting packages come with free SSL and installation service of your purchased UltimateWB software onto your web hosting account.