Imagine I am sitting here in Massachusetts and I want to see your profile photo. That photo has to be somewhere on the web in order for me to see it. I can't look into the insides of your computer, thank goodness.
So you have to put the photo onto the web somewhere, in order for me to see it.
Photobucket is a free place to store photos. You can use any other place you have access to. There are lots of options. But it does have to be somewhere on the web - otherwise I won't be able to see it from my home computer.
Does that make sense?
Some forum systems might let you put your photo onto their actual forum server, but we don't allow that here for safety reasons. Someone could load up a pornographic photo and then we'd be liable for it.