Help with Signatures

There is just no help or documentation about implementing DKIM on my DNS server and linking it to my AlphaMail. Overall the current Signatures pages is just confusing: how do I check if I modified my DNS correctly? What's the difference between Name and Domain? Shouldn't it be Subdomain and Domain? How many TXT entries should I add? One per project? If so, how?
At least one page in the docs should be written towards this, not just a link to a Wikipedia definition.