For Creating the Bootable USB flash Drive you needs the iso image file, always check the iso image file size because you needs the more than file size flash USB drive i.e. if your iso image file is 4GB than you needs the 8GB flash Drive to make bootable USB.
For creating Bootable USB you need a best tool so you can use Rufus. This tool is free and very easy steps to create a bootable drive.
Step 1 – First you needs to open the rufus software after installation.
Step 2 – Now you needs to browse and select the iso image file which you want to make as bootable.
Step 3 – Choose the Partition scheme i.e. MBR or GPT .Now days we always use the GPT partition so choose by default as it is.
Step 4 – Now click on START button than it will start to make bootable USB Drive by using iso image after all the files written in USB drive by rufus software. It will show message in the bottom Finished, than you have to eject your USB bootable drive from the System.