Hello what are the advantages of making a dns server on the same pc with the active directory domain controller?

Well the first is obviously you'd only have 1 server. It depends on what your needs are really, what services you plan on running. Some services conflict with each other (they will tell you this when you try to enable them) so in some cases you can't run DNS on the same machine as "some other service". Of course you need DNS to run AD, it won't install unless you have it enabled on that server, or another is available on the network somewhere already.