You will need a computer with an internet connection. You will have to download the installation media from the Download page of the Archlinux.org. It is better to download from the official site rather than a third-party mirror server. It is recommended that you checksum the download with the iso signature also downloadable from the Download page.
I usually download using the magnet link (through torrent, using a torrent client) because it's faster and it's my way of giving back by seeding it for a while. I keep the latest .iso and the .iso.sig files in its own directory. Then do the checksum with # gpg --keyserver-options --auto-key-retrieve --verify archlinux-yy-nn-dd-x86_64.iso.sig
The Straight Forward Easy Way
We will use the dd command. It will overwrite the entire USB flash drive and any data will be deleted. You won't be able to write any data when using the installation media. You can zero out the USB flash drive if you want to reuse the device with # dd bs=512 if=/dev/zero of=/dev/sdx count=1 status=progress oflag=sync.
To create the Archlinux installer USB device type the command # dd bs=4M if=/path/to/archiso/archlinux-dd-mm-dd-x86_64.iso of=/dev/sdx status=progress oflag=sync.
If You Are In A Linux Distro With GNOME
You can use nautilus and gnome-disk-utility. Just right-click on the .iso file and choose Image Writer. Image Writer will use the entire USB device. You will end up with a live media and a USB drive where you can still save personal files.
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