The OpenMediaVault installation is documented here as several points have to be considered. You should be familiar with Debian or be familiar using linux system commands on the command line.
download and install the firmware supporting Debian
Refer to Debian Installation for the firmware supporting Debian download and installation procedure.
You can install OpenMediaVault with the following commands. Please keep in mind that kernel modules installation is mandatory, and as such is included on this script too:
wget https://raw.githubusercontent.com/gnubee-git/gnubee-git.github.io/master/debian/omv-jessie-install chmod +x omv-jessie-install ./omv-jessie-install