When a computer starts, it does it using the operating system on the hard drive but it also has the ability to boot from a CD, USB drive, network server, etc.. Here's how to start the computer on a bootable CD (like Ubuntu).
On a Apple Mac computer
Something specific to Apple, you should insert the CD and shutdown the computer. The you can press the power button and immediately press and hold the C key on the keyboard until the CD starts.
On normal PCs
Many computers are configured to start automatically on a bootable CD if there is any one in the drive. Try to insert the CD and restart your computer. If it starts normally without asking anything, it didn't work! So you'll have read the rest of this page ..
Choose the CD in the BIOS
This is where it goes bad. Our editorial team would like to give you some simple steps .. Unfortunately this is impossible because they vary depending on the computer. What does not vary is that each computer has a BIOS in which it is possible to modify the boot settings so that the computer tries to boot the CD before on the remaining parts.
To access the BIOS, you must press a key on the keyboard at startup while the screen is black, however, this key varies from one computer to another, even if the Esc, F1, F2, F10, F11 and Del keys are the most common. Pressing these keys simultaneously is ugly but very favorable to success. But you can also take a look at the screen at startup, very often that key is briefly revealed as you can see in the following picture.
On some computers, your life will be easy and you'll immediately get on a list in which the CD will be displayed, you will only have to choose it with the arrow keys to start it. Otherwise you'll end up in the BIOS in which it is possible to move through the menus using the arrow keys. The keys to use to change options are always displayed at the bottom or somewhere in a corner of the screen as like the given example.
You should look for something containing the word boot in the menus, such as "Boot sequence". This is where you will find a startup list. If you can put the CD drive to the first position in that list and save the changes, the CD will boot else on next restart! Be careful however, take note of every changes you made in case you would have to revert them. If you believe that you changed some option by mistake, quit without saving and start over, its better to avoid problems.