Step1
Open your internet browser.
Step2
Type "www.linux.com" into your adress bar.
Step3
Go to the Downloads page.
Step4
Choose your version of linux. I will assume that you are using Ubuntu, the version at the very bottom of the page.
Step5
Go to the download page for Ubuntu, It should be right below the name.
Step6
Enter all of the options that you would like to use, and select the location nearest to you so that it downloads as quickly as possible. Then click "Download now"
Step7
The download may take a while, it is rather large, be patient.
Step8
Burn the ISO image (NOT THE FILE) to a blank CD, you can use a variety of programs, I use DVD Decryptor, it is free and does what it has to. If you would like to use this, search it in Google and download it, then go to Mode/ISO/Write. The press burn now.
Step9
Once the burn is complete, shut down your computer and take out the disk. (Not in that order, but I hope that you get the idea)
Step10
Turn on your computer and go to your BIOS mode setup. To get here, there should either be an instruction on the screen as the computer is turning on or you may need to continually press the delete key as it is turning on. If neither of these work for you, look up how to do it on your specific computer.
Step11
There should be a section of the bios menu that says "BOOT". Navigate to there using the arrow keys, and set the CD drive to start up first, before the hard drive. or the DVD Drive, depending on which drive you prefer to use.
Step12
Insert your disk into the drive that you selected.
Step13
Go to "Exit and Save Changes". When prompted, press yes. The computer should restart, leave it. If you are prompted to press a key because there was an error, go ahead and press it.
Step14
Linux should be starting up, hope I was helpful!