We pick f.root-servers.net, one of the 13 root servers (1), and ask it about getran.detran.df.gov.br and learn that br is delegated to six name servers (2), so we ask c.dns.br where we learn that df.gov.br is delegated to four name servers, including name2.gdfnet.df.gov.br (3), so we ask that one and learn that detran.df.gov.br is delegated to two name servers (4), so we ask ns2.detran.df.gov.br and get the following answer:
The two name servers ns1 and ns2.detran.df.gov.br together
All of the one domains that use the two name servers ns1 and ns2.detran.df.gov.br together, hereafter referred to as "name server group 1", use only the mail server mail.detran.df.gov.br.