1 Set up your repository

Create a public repository named pages to make the site available at the main subdomain.

Create a branch pages in a public repository:
git switch --orphan pages
git rm --cached -r .

2 Upload your files

Push your static content, HTML, style, fonts, images or anything else.

3 You're done!

Access your new website using this link:
https://USERNAME.codeberg.page[/REPOSITORY][/@BRANCH]

To use a custom domain, create a file .domains in your repository with the domain name you wish to use.

Then, add a DNS record for that domain:
CNAME [[branch.]repo.]user.codeberg.page.

Or for apex domains where CNAME doesn't work:
ALIAS codeberg.page.
TXT [[branch.]repo.]user.codeberg.page

If ALIAS isn't supported, use A & AAAA instead:
A 217.197.91.145
AAAA 2001:67c:1401:20f0::1
+ TXT as above