Just received my macbook air and discover that i can't run port command because of /opt directory not exists. Is it normal? (OS X 10.9)
Yes, OS X does not come with anything in /opt or even the directory itself. I presume you're looking for MacPorts, which is a 3rd-party package manager that installs
Various other apps can place files in /opt though. For example, even though I've never had MacPorts, I have the /opt directory and it contains the X11 directory.