Um...generally, forums don't take a new guy and instantly promote them to staff.
I think the process to becoming a staff member generally goes something like this:
1. Join the forum.
2. Post in the forum so that people learn who you are.
3. Conduct yourself well and make thoughtful posts so that people recognize you as a contributing member of the forum.
Wait until a position opens up, at which point the staff will contact
you and ask if you're interested, not the other way around.
5. ???That's really all you can do. You don't "choose to become a member of the staff." I'm sure you're a great guy and all, but you have one post and absolutely no one on the forum knows you (unless they know you from outside the forum). We don't know what you're actually like at all, so you have to build up that trust before you can even think of becoming a staff member.
And it might take a while. There was a forum I frequented for four years before I was promoted to staff--and that was only because the entirety of the old staff quit and they had open applications. Don't hold your breath quite yet.