Select the USB drive from the "Device" list (make sure it's the right one!)
Press the "Select" button on the right and choose the ISO image you downloaded
Leave the rest as defaults.
You must download and install the livecd-tools as root, if they are not already installed: dnf install livecd-tools
Insert blank USB drive (4gb at least)
/usr/bin/livecd-iso-to-disk --format --noverify \
--force --reset-mbr \
--efi image.iso /dev/sdX1
Where the X in /dev/sdX1 is the drive letter of the USB drive.
Be very careful and make sure you have the right drive letter or you could clobber your
hard drive. (Often, doing "dmesg" right after inserting the USB drive will give you an indication
as do the correct drive letter (example):
[836008.107744] usb-storage 1-7:1.0: USB Mass Storage device detected
[836008.107803] scsi5 : usb-storage 1-7:1.0
[836009.445872] scsi 5:0:0:0: Direct-Access SMI USB DISK 1100 PQ: 0 ANSI: 4