Visit the Downloads link from the main page. Also check on the appropriate directory for the corresponding md5sum file to verify the correctness of the file you downloaded.
$ cat Obarun-JWM_x86_64-2019-05-3.iso.txt
$ md5sum Obarun-JWM_x86_64-2019-05-3.iso
The signature should be identical, otherwise the download was not correct.
Please note that Obarun Linux ISOs are USB bootable by default, so you just need to write the image to the usb/cd/dvd drive with dd, no special tools are required.
First, identify your usb's current device name. At a plain shell prompt:
$ sudo fdisk -l
From the output, you might determine that the device name is /dev/sdc or otherwise, but for safety's sake, it will appear here as /dev/sdx.
Other utilities that could help identify the device name for your usb key include Parted, Gparted or through command like:
$ sudo parted -l
$ ls -lah /dev/disk/by-uuid)
Then, ensure that that device is unmounted. Change sdx in the following line to your usb's device name:
$ sudo umount /dev/sdx
Change to the directory where your .iso was downloaded to. For example:
$ cd ~/Downloads
Warning: The following instruction will destroy all data on the device is being referred to. Proceed with caution.
Change the following line to display the correct image name and correct device name. Note sda3; sdb2, sdc1, etc. would be incorrect as they refer to partitions.
$ sudo dd bs=4M if=Obarun-JWM_x86_64-2019-05-3.iso of=/dev/sdx status=progress oflag=sync
If you must use ms-Windows to write the image and are looking for a GUI based app, USBWriter is proven to work on pendrives (USB sticks) and even SD cards. Most USB writers for Windows that promise to get the job done tend to mangle the data in such a way that the media isn't bootable at all.
In general it is advised to follow the arch-linux wiki on the subject.