The cloning method described in the answer by ovc is very reliable, when used correctly, and it works with all hybrid iso files. Most iso files of modern linux distros are iso files.
dd is a cloning tool. It is very powerful but also dangerous, because it does what you tell it to do without questions. So if you tell it to wipe the family pictures ... and it a small typing error away. It has earned the nickname 'data destroyer'.
Instead you can use tools, that perform the same task under the hood, but help you select the target device and double-check that it is the correct drive. Starting with Ubuntu 16.04 LTS, the Ubuntu Startup Disk Creator, alias usb-creator-gtk, uses the cloning method. Disks alias gnome-disks can also clone from an iso file to a target device, usually a USB pendrive or memory card. These two tools are built into Ubuntu.
There are also other cloning tools, that can be installed into Ubuntu or Windows. mkusb can clone iso files and compressed image files. It can also create persistent live drives, and it can restore a USB boot drive to a standard storage device after the installation.
Win32 Disk Imager is a cloning tool for Windows, that can help you create a USB boot drive with Ubuntu.
There are also many tools, that can create USB boot drives by extracting the content of the iso file to another file system and install a bootloader to the target device. Several of these tools work well and can be recommended, for example Rufus and Unetbootin.
But when the boot structure of the iso file changes (in a new version of Ubuntu), these extracting tools will have problems, until they are modified to recognize and manage the new boot structure. Older versions of the Ubuntu Startup Disk Creator (before 16.04 LTS) are affected by several bugs because of modifications of the syslinux boot structure in BIOS mode.