dmd download sig file, how do I use it

[Ali]

Hi All,

The DMD download is accompanied with a sig file
How exactly do I use this sig file
I am assuming I can use it in place of checksum to verify the 
download

And to be honest, I have almost zero knowledge for gpg and 
encryption
I googled a little but, didnt exactly find what I was hoping to 
find

I tried the following command
> gpg --verify dmd_2.079.0-0_amd64.deb.sig dmd_2.079.0-0_amd64.deb

which returns

  gpg: Signature made Fri 02 Mar 2018 01:47:57 PM EST
  gpg:                using RSA key B273811612BB1939
  gpg: Can't check signature: No public key


I guess this means, the file is not verified
So how can I do a complete verification?

I also downloaded the keryring file, from link in the download 
page
but also couldnt figure out how to use it

Any explanation of how this gpg sig key works and how to use it 
to verify the download
would be appreciated

thanks