Help with SubDomain

If this isnt the right place please can a mod move this to the correct section.

I am a freelancer trying to create a subdomain for my website that is pretty much an onboarding section for my clients with payment, contract etc.

But have piled through videos and shit and am still so lost.

Bought my domain with godaddy and made my website on carrd. If anyone can help me out id appreciate it.

Thank you in advance.

Replace your web site to new domain name?
Or, please elaborate more what you mean.
If you need your web site to be opened on new URL you can adjust redirect for now.

Do you have cpanel? Custom website or WP?

You'd better post more details regarding your plan here.
Also you always have an option to contact your domain name registrar / web hosting provider and ask them for help.
I think that will not be a problem for them at all.
In this case you will have everything done properly.