Sheetmetal welding question

[ashx2]

Forgive the ignorance, but I'm still learning on this.......

When you guys are welding, say, a rocker panel into place for instance......

Are you using a wire welder or what? Also when I see the pics I see that you're tacking say every couple of inches......do you go back and "fill" the rest of the bead and then grind it down?

Just not quite sure how this is done, and lord knows I need to get some information......I'm going to have to do it in the future.

Thanks guys!

Greg