This directory /tmp/rpm contains all the packages downloaded but after this exercise i tried to run createrepo and /tmp/rpm with root and there is an error "command not available "
Hmm, how about actually reading what i write for you:
So, how about downloading it? You can find at rpmfind.net or you can get download instructions from createrepo.baseurl.org, which were about the first and the eighth hit when i entered "package createrepo" into my search machine. It is a becoming trait of a systems administrator to be able to get (on his own) the information he needs to do his work.