"zpool create" will create a pool of disks to use to create filesystems.
"zfs create" will create filesystems within the pool.
# zpool create tank mirror c4t1d0 c4t1d1
This zpool command creates a new pool called "tank", mirroring two disks. It also creates the "top level" filesystem, also called tank and mounted at "/tank".
# zfs create tank/foo
This zfs command creates a new filesystem, mounted by default at "/tank/foo".
If you don't have disks to play with, you can try out zpool and zfs commands by using file-based pools. Use "mkfile" to create new files (e.g. mkfile 500m /var/tmp/a /var/tmp/b), and then use those files to create a pool (zpool create tank mirror /var/tmp/a /var/tmp/b). Note that file-based pools are for testing purposes and do not have the performance needed to support databases. But they do give you the opportunity to try out different commands and see their effects.