Please just follow the instructions:
If you look about 100 pixels up, there is a banner with information, and a link that describes you exactly what to do.
Just follow the instructions.
Which are all entirely irrelevant for requesting an SSL certificate. All you need is to be able to setup CNAME records. Which is what the instructions tell you to do.
By adding the right CNAME record. Which is what the instructions say.
Of course it shows junk, because it’s the bad value. You need to fix it by adding the right CNAME record. Which is what the instructions say.
It says Not Secure because your website doesn’t have HTTPS, which is doesn’t have because you haven’t installed a certificate, because you don’t have a certificate, because you haven’t setup the CNAME records yet.
Just add the CNAME records as instructed.
It’s not a nameserver issue. For the purposes of getting an SSL certificate, you can use whichever nameservers you want. All you need is to add the CNAME record to them. As instructed.
Just follow the instructions. It will work. Don’t try and make up your own explanations about nameservers or what the current record means. Just. Follow. The. Instructions.