I'm using cloudflare as my DNS, and it's literally just:

• Create an A record.
• Set the name to "*" (without quotes)
• Set the IP to the appropriate server
• You may want to untick the proxy, depending on what you're hosting. If it's web stuff only it's fine, but if you're doing anything else as well it'll get in the way.

On the letsencrypt side, it's pretty similar. Create a certificate with doman.name and *.domain.name (if you want them to share a cert) and you're off.