Can’t register new domain

I want to forward my email with new domain. Since I’m pretty new to this topic please correct me if I’m saying something wrong. To register my new domain I was using Namecheap and first I could also create my new domain. However after that I couldn’t find my domain in the dashboard under "domain list". Namecheap said that I had to add a TXT record first. Is this necessary or did I do something wrong before? I’m wondering about that because I have watched several tutorials and the domain always appeared in the domain list there.
I have also looked in the help section and there I have found a not very helpful guide. That guide just sais: change your TXT record. But how can I do that? Do I have to use one of these expensive tools like CPanel? If possible I would like to do it for free.

Thank you!