I have my forum set up...lost on how to skin/add pics

[twiskus]

Okay, I am not the dumbest person in the world, but definitely not the smartest when it comes to computers/programming. I have my forum with 4.0.6 up and running and have all of my sections. Now I need to customize it, as it lacks any pizzazz so to speak. I have a Mac and am operating on 10.5.x I guess I thought this part would be a little easier (and maybe it is) but I just can't figure it out. I have set up the following accounts:

I have got my FTP set up through file zilla
I have my account for webmaster tools set up
I know how to access my cpanel.

Okay, I know how to log onto the admin section of my site (where I was able to set the initial forum up) but I have no idea how to use the plug-in options or any of that stuff. I was told I needed an FTP account to add stuff to my website, is this correct?

My main question...how do I customize my forum?

TIA

Trev