How can I subscribe to comp.lang.c using Mozilla Thunderbird?
I do not understand such newsgroups much (I have no idea why they do not have a unique server address).
What should the correct Server Settings look like?

How can I subscribe to comp.lang.c using Mozilla Thunderbird?
I do not understand such newsgroups much (I have no idea why they do not have a unique server address).
What should the correct Server Settings look like?

You would need to connect to an NNTP server before you can subscribe to the comp.lang.c newsgroup. They used to come with service from your ISP but that is quite rare these days, but could be simple as news.yourprovidername.com. Or perhaps there's a free NNTP server out there?
Next, once you have a NNTP server name, enter that name for Server Name (where the screenshot now erroneously shows the group name comp.lang.c).
Finally, Thunderbird will show you a list of all groups, where you can select the group(s) you want.
Otherwise you could use Google Groups in your browser.
Get a news server. Try http://www.elfqrin.com/hacklab/pages/nntpserv.php for some free ones. Add one as your nntp server.