Do not be confused by the term "live CD," unlike before, booting using Ubuntu is only available via real CD. And booting using USB back then is not possible. Thank's to the advancement of technology, many developers are making innovations, and the booting using USB devices is now possible.
For this tutorial, we will need:
How to make Ubuntu Live CD using USB and Rufus
1. Download and install first, Rufus.
2. Now, download the Ubuntu image also.
3. After download and installation, insert your USB flash drive in your USB port. Make sure your USB device does not have any of your essential files. If so, backup first all your files inside your USB device because all of it will be removed later.
4. Now, open Rufus and click the CD icon.
5. Browse for the Ubuntu iso image file that you downloaded earlier. Select it, and then click the Open button.
6. After that, click the Start button. Just leave every other field to its default state.
7. A warning saying "all data on device "name of your USB device) will be destroyed." Just click the OK button to continue.
8. Wait for creating a file system process to finish. IT may take a while, depending on the Ubuntu version that you have. The smaller the file size, the faster it ends, and vice versa.
9. When it finishes, click the Close button to exit Rufus.
10. Restart your computer and make sure to boot from your USB device. You can try pressing any of your computer function keys (F1 to F12) to be able to access your boot menu.
11. When you successfully booted using your USB flash drive that contains your Ubuntu live CD, you will see the image below. Just click the Try Ubuntu button.
12. And the image below is a sample Ubuntu environment from a USB live CD.
13. Done! Just click the Gear icon located in the upper-right corner of your screen to Restart your PC.