Here is the sequence: Attach the halyard to the spinnaker's head, the sheet to the spinnaker's clew, the downhaul to the spinnaker's tack where the TACKER has already been shackled, pass the TACKER around the furled headsail, clip the snap shackle onto the spinnaler's tack and hoist away. Trim the sheet and the downhaul and you are sailing. The downhaul, in most cases, can be replaced by a rope pennant always on the spinnaker's tack, making the operation even easier.
Of course you can fly a spinnaker without a pole and without the TACKER, but bear in mind that a conventional spinnaker is designed to fly a couple of feet above the lifelines. Its foot (between the clew and the tack) should always be horizontal. Securing the spinnaker tack to the deck is not the best way to set the sail. It is too low and the spinnaker will chafe on the bow pulpit and lifelines. If you add a pennant or a downhaul, the spinnaker falls off to leeward and the pennant chafes on the pulpit and the sail looses its shape.
That's when the TACKER saves the day. It holds the tack, and the luff, of the spinnaker close to the centerline of the boat and it can be adjusted up and down with the downhaul for a perfect trim.
The NEW Tacker is now fitted with a snapshakle, which allows the operator to blow the tack of the spinnaker, making it even easier to control the sail.