Is there a specific format a USB needs to be to boot from?
The solution depends on which operating system are you running now (Ubuntu, other linux, Windows MacOS). You need a tool to create a USB boot drive, and there are different tools for different operating systems.
Cloning tools are simple and reliable but it is also possible to use extracting tools, if they are well maintained (updated to work with new versions of the operating system to install).
Most modern linux iso files are hybrid iso files. Such files can be burned to a DVD disk and cloned to a mass storage device (USB stick, SSD, HDD, memory card) and the target device will become a bootable drive.
You can clone from a current Ubuntu iso file to a USB stick and use that USB stick to boot Ubuntu live and install Ubuntu into the internal drive.
dd is a cloning tool, but it is risky because it does what you tell it to do without any question. If you tell it to wipe the family pictures it will do it. A minor typing error may create chaos. You must be very careful, check and double-check that everything is correct before you press the Enter key.
Instead I recommend a tool with a final checkpoint,
in Ubuntu 16.04 LTS and newer versions: Startup Disk Creator alias
usb-creator-gtkin Ubuntu 14.04 LTS and newer versions: Disks alias
gnome-disksin Ubuntu 12.04 LTS and newer versions and other main linux distros: mkusb
in Windows: Win32 Disk Imager
in Windows: Rufus - an extracting tool and a cloning tool
in MacOS: Unetbootin - an extracting tool (not a cloning tool)