Wildcard subdomain DNS records point all subdomains that are created for a specific domain name to a specified location, either an IP address or specific subdomain.
When this record is in place it's not necessary to individually specify where subdomains should point, as the "wildcard" directs all of them.
Wildcard DNS records can be added with A or CNAME records. You will need to add two records. The first one is an A record to direct the naked domain (e.g. mydomain.com). This determines the target where the domain points to, usually a website.
For this first A record you will leave the Hostname blank. It will be filled in with @ once it's saved. Add your site's IP address (something like 22.214.171.124) in the Value field. TTL can be left as is at 3600.
The second record can be either an A or CNAME and includes the asterisk ( * ) as the wildcard in the Hostname field to specify that it directs all subdomains of the domain to the specified IP address or provided subdomain. E.g. *.mydomain.com would direct blog.mydomain.com, shop.mydomain.com, help.mydomain.com, and any others created to the same site or page.
It could be an IP address if an A record is used (something like 126.96.36.199), or it could be a specific page URL if a CNAME record is used (e.g. example.mydomain.com). Again, TTL is left as is at 3600.