odoo-bin needs to be run from the directory where it exists in your file system OR added to your $PATH

for instance my odoo-bin is within 

/odoo/odoo-server/odoo-bin

if I cd into /odoo/odoo-server I can then run:

./odoo-bin scaffold mymodule /odoo/custom/addons/

I need the ./ in here because /odoo/odoo-server is not in my $PATH

where /odoo/custom/addons is my directory for custom made modules so as not to interfere with odoo base modules. This can be setup from the command line and by editing /etc/odoo-server.conf (my installation is on Ubuntu fyi)