This tutorial is to show you how to install a SoftEther VPN on Ubuntu 12.04 & Ubuntu 14.04.
After installing a fresh copy of Ubuntu or your machine, run following commands to update the packages.

apt-get update -y
apt-get upgrade -y

After updating add SoftEther PPA:

add-apt-repository ppa:dajhorn/softether

Update package list again & install softether package.

apt-get update
apt-get install softether

After installing run following commands to check for any errors.

vpncmd

Select option 1.  And press Enter for the rest. Then run command check.

check

If you get output same as above image, then you have successfully installed SoftEther VPN server on your machine.