The iActive (B200/B253) bedhead should come with the following:
8 x Long bolts with nuts
2 x Brackets
4 x Short bolts
Additionally, you will need a socket and wrench (or similar) for assembly.
Start by attaching the brackets to the bedhead using the short bolts. Have the open side of the brackets facing inwards.
Move the headboard into place at the head and using the longer bolts and nut secure 4 bolts per-side to secure the bedhead to the base. Use appropriate tools to tighten.