What is difference between Wildcard SSL and just normal SSL?
At a very high-level, a "Wildcard" SSL certificate would allow
<any-subdomain>.example.com. Whereas a "normal" SSL cert would be limited to just a single host. eg.
my-subdomain.example.com, but not both.
However, many "normal" SSL certs do cover both the apex and
www subdomains these days. ie.
www.example.com - since this is a very common requirement.
Or were you after a deeper explanation?