Now that you have the live cd, pop it into your computer. It should boot up from the cd, but if it doesn't, mess around with your bios. It should be set to boot from the cd drive first. You will see a screen with an option on the top to start or install ubuntu. Press enter, but don't worry, it's only doing the starting part. Once it boots up, which will be a slow on an older computer, there will be a screen that looks like the image above. You can try ubuntu out, but then double click on the install button.