We need to know where to find the root nodes of DNS, the root nameservers. This file is to do that. You put it in the directory you named in named.conf, as follows:
; ; There might be opening comments here if you already have this file. ; If not, don't worry. ; . 6D IN NS G.ROOT-SERVERS.NET. . 6D IN NS J.ROOT-SERVERS.NET. . 6D IN NS K.ROOT-SERVERS.NET. . 6D IN NS L.ROOT-SERVERS.NET. . 6D IN NS M.ROOT-SERVERS.NET. . 6D IN NS A.ROOT-SERVERS.NET. . 6D IN NS H.ROOT-SERVERS.NET. . 6D IN NS B.ROOT-SERVERS.NET. . 6D IN NS C.ROOT-SERVERS.NET. . 6D IN NS D.ROOT-SERVERS.NET. . 6D IN NS E.ROOT-SERVERS.NET. . 6D IN NS I.ROOT-SERVERS.NET. . 6D IN NS F.ROOT-SERVERS.NET. G.ROOT-SERVERS.NET. 5w6d16h IN A 126.96.36.199 J.ROOT-SERVERS.NET. 5w6d16h IN A 188.8.131.52 K.ROOT-SERVERS.NET. 5w6d16h IN A 184.108.40.206 L.ROOT-SERVERS.NET. 5w6d16h IN A 220.127.116.11 M.ROOT-SERVERS.NET. 5w6d16h IN A 18.104.22.168 A.ROOT-SERVERS.NET. 5w6d16h IN A 22.214.171.124 H.ROOT-SERVERS.NET. 5w6d16h IN A 126.96.36.199 B.ROOT-SERVERS.NET. 5w6d16h IN A 188.8.131.52 C.ROOT-SERVERS.NET. 5w6d16h IN A 184.108.40.206 D.ROOT-SERVERS.NET. 5w6d16h IN A 220.127.116.11 E.ROOT-SERVERS.NET. 5w6d16h IN A 18.104.22.168 I.ROOT-SERVERS.NET. 5w6d16h IN A 22.214.171.124 F.ROOT-SERVERS.NET. 5w6d16h IN A 126.96.36.199
This file simply enumerates the rootservers and their addresses with standard NS and A records. The file is called "hints" because its contents are not taken as gospeleverything in it is simply hints. Your named will verify how matters really stand and also develop a preference for one of the addresses based on its track record for response time.
Even so, the file still needs to be maintained. This will ensure that after several years of neglect, the file does not fall completely out of sync with reality and no-longer provides a usable starting point for your named to resolve queries.