Often times, the connections for a metal gate do not fit a wooden post. In order to attach the metal gate to the post, it is necessary to adjust the attachment fittings and drill through the post. Then, you can connect the metal gate to the wooden post.
Take the attachment fittings for the metal gate and bend them to the dimensions of the wooden post. This generally involves taking a c-shaped piece of metal and making it into half a square. For the metal post, the attachment would go all the way around the post. For the wooden post, the attachment will only make it halfway onto the post.
Clamp the attachment onto the post at the appropriate places where the gate requires the attachments to be. Drill through the holes in the metal attachment through the post and out the other side.
Put the bolt through the hole and attach with the washer and nut on the other side using the wrench. Make sure that you tighten the bolt so that the gate does not sag.