The hostname is the name of the record that you are creating, e.g. mail. In a CNAME record, the hostname is known as the alias and the target is the canonical name. Those terms could also have different meanings, depending upon context.
Can you tell us what you are trying to accomplish? If you are following a guide, can you share a link to it?
I received some records that I need to update for my new SSL certificate to be issued. They told me the type should be CNAME, It refers to “Other Host”, and the host name and alias values are a string of random characters. I am supposed to update these DNS records under my nameservers, but I don’t know where to enter the values
What they have labeled as an alias is the canonical name, not an alias. Don’t be misled by their improper terminology.
Create a new DNS record using the hostname as the name and what they are mistakenly calling the alias as the target. Be sure that record is set to DNS Only. That last part is critical.