This technical note provides a link to PDF files that contain instructions for creating a GNU/Linux system that has an encrypted root partition.
These instructions (in a PDF and formatted for printing) describe a process that will install OpenSUSE 13.1 with an encrypted root file-system. The process, and the level of protection it provides, are for people who want the information on their computer to be secure if it is stolen by ordinary thieves. The significance of "ordinary thieves" is that they are unlikely to have the skills or inclination or resources to break any encryption; most likely they'll just want to sell the computer for quick cash. By contrast if your computer contains the sort of secrets that government agencies might want to look at then it might need more protection than is described in the linked article.
The process can be used to create an encrypted operating system on an internal hard-disk, externally connected USB disk, or on a USB memory stick. The process should work with laptop or desktop computers. The instructions assume that the user will install LXDE as the "graphical user interface", but LXDE is not necessary and the user could choose to use KDE or Gnome, or to use no graphical user interface at all.