Hi Max - Flow is a tool that was developed for MoI version 3 - MoI version 2 does not have it.

I have new documentation for v3 on Flow here:
http://moi3d.com/3.0/docs/moi_command_reference8.htm#flow

It's located under Transform > Deform > Flow.

You can order an upgrade from v2 to v3 here:
http://moi3d.com/purchase.htm

Also the v3 beta release is still currently going, you can download the v3 beta by putting in your v2 license key and run that until it expires a couple of months from now. That's available here: http://moi3d.com/beta.htm

Hope this helps!

- Michael