Want to replace old site with a WP site, hosted by 1and1, but . . .

My former web designer is gone, and I am baffled. Please pardon my rookie status.

I have three websites (hosted by 1and1). Two are WordPress, and I can easily add content to these online. But the third is not WP, is obsolete, and requires ftp.

I would like to start the site from scratch using WordPress — my rookie question is how to do this?

Customer support at 1and1 unhelpfully replied “if you are still working on a website and doesnt want to publish it using the main domain name, you may create a subdomain (example: test.domain.com)” — I don’t even know what that means.

I assume (despite my history of failed assumptions) that I do not need to download WordPress to my laptop, but can select theme and construct pages online. I just do not know how to do this, and ,y second assumption is that the WordPress forum will give a better answer than 1and1.

Thank you.