Rufus is one of the many applications to create bootable USB drives. Rufus website can be found here.
How to use Rufus:
Download an .iso file you want to flash on a USB drive
Start Rufus
Select the USB device on which you want to flash the .iso file
Press the SELECT button and select the .iso file
You can change the partition scheme, target system and/or persistent partition size, however, Rufus can detect this automatically so you should not change the selected options.
Rufus will also fill in a volume labele, however, you can modify to your needs.
Also leave the File System and Cluster size options as is as Rufus will preload it for you.
Press the START button: accept the default (recommended) write mode of the image in the popup window.
Press the OK button
Accept the next proposal to download extra files for Linux, if asked.
A final warning window will appear to indicate all data on the USB device will be destroyed. Press the OK button.
Rufus is going to flash the .iso file onto the USB. This can take a while