A way to design the site before it goes live.

Site URL: https://www.portmandoors.co.uk/

Hello.

The company I work for wished to spruce up their website to look more modern and chic. I was considering transferring the domain over to Squarespace to do so. However, I'd rather the site were inaccessible for our potential customers for as short a time as possible. As such, before I continue I want to know whether it is possible to design your site with Squarespace before the domain transfer or in some other environment that wouldn't remove the site's current content in the process. Then, when completed, I could go straight from the old site to the new one, if you follow. 

Is this possible? Thanks.  

Every new SS site build comes with a two week trial. No upfront credit card needed. After two weeks you would need to make a payment but the site would still not be live until you move your domain. Nothing takes place to the original site at all, it still operates until the domain is repointed or transferred to Squarespace.

Could you explain in detail the comment "move your domain"?

I am in a trial, but have paid for my website now. I don't understand how to do this.