Join with a slip stitch or join with a needle or join with a hook … choice is yours.
With a slip stitch : you would join your circle with a slip stitch into the top of the chain 2. End of the story.
With the hook … same technique as with a needle:
- Remove your hook; cut the yarn and pull it all the way through the stitch/loop [where the hook was].
- Insert your hook below both loops of the next dc [first DC], from the back to the front.
- Grab the yarn and yarn over and hook it through the stitch so that it is pulled from the front to the back and pull gently.
- Insert your hook in the last DC you made – through the back loop only, from front to back, and pull it through.
- Grab the yarn and hook it through that back loop [pull the tail end yarn all the way through].
- Weave in yarn end. And voilà.