First, install the OVF Tool.
Then, run the tool. The syntax looks like this:
/Applications/VMware\ OVF\ Tool/ovftool --acceptAllEulas /path/to/file.ovf /Users/username/Documents/Virtual\ Machines.localized/vmname.vmwarevm/vmname.vmx
If you see errors about virtual hardware not being supported, you can add the –lax parameter to the command line.