Using command lines:
1. On Linux/Ubuntu Terminal
sudo umount /dev/sdc<?>
sudo dd bs=4M if=input.iso of=/dev/sdc<?>
where input.iso is the input file, and /dev/sdc<?> is the USB device you’re writing to. <?> is a number. Look it up.
2. On Windows CMD
•Insert a USB flash drive and open CMD
•Type ‘diskpart’ and hit Enter.
•Wait for a while until the DISKPART program run.Type ‘list disk’ to view active disks on your computer and hit Enter. There would be seen that the active disks shown as Disk 0 for hard drive and Disk 1 for your USB flashdrive with its total capacity.
•Type ‘select disk 1’ then hit Enter.
•Type ‘clean’ and hit Enter to remove all of data in the drive.
•Type ‘create partition primary’ and hit Enter. Creating a primary partition and further recognized by Windows as ‘partition 1’.
•Type ‘select partition 1’ an hit Enter.
•Type ‘active’ and hit Enter. Activating current partition.
•Type ‘format fs=ntfs quick’ and hit Enter.
•Type ‘exit’ and hit Enter.
Else you have windows applications like rufus which is a utility helping you to create a bootable usb using iso images.
On linux you have built in application, usually.