How to format external drive into ZFS?
The getting started page you posted a link to explains how to create a simple one disk pool.

This is the only thing you need to do. Creating a pool will automatically create a file system with the same name as the pool, which is what you call formatting a drive.

In your case, you can run from the command line:

diskutil partitiondisk /dev/disk5 GPTFormat ZFS %noformat% 100%
zpool create extdrive /dev/disk5s2


and you'll have a new volume named extdrive available.

If you happen to run software with inconsistent file naming, like Adobe products and possibly Nikon capture, you might want to create a dedicated file system with case insensitivity set using something like:

zfs create -o casesensitivity=insensitive -o normalization=formD  extdrive/data