To boot from the live CD/DVD, place it into the CD/DVD drive and then restart your computer. Most computers will automatically boot from a CD drive if they detect a bootable disk. If not, you may have to change the bios settings so it boots from CD/DVD before the internal hard drive, or alternatively you may have to press a function key after turning the computer on to bring up a list bootable devices.
Unfortunately neither the bios or the boot list are accessible to someone using a screen-reader, so you may need sighted help to change the bios settings and/or learn the keystrokes to bring up the boot list and select the CD/DVD drive.
If you don't have an internal CD/DVD drive then you can use an external USB optical drive, or alternatively download the USB version of Vinux and boot it from a USB pendrive.
Please note that since Vinux 4.0 the images can be written to optical media as well as USB sticks.
When the system finishes booting you will hear "Welcome to Orca!".