no one has mentioned that fact that you should have a decent mask too
and DON'T look at the sparkaly bits when you are welding without the mask, it hurts your eyes, sometimes for days

i've got no pics of when i welded up my sills but they were rotten to the core, floorpan and sill were not joined by anything so out came the grinder and the welder and everything else

if you are thinking of welding in a difficult place then it's best left to the pros, but if it's the open end of a panel then have a bash yourself

but make sure you practice with a bit of old metal first, that way you can set the mig up to do whats right for you, rathe than flap about with settings while on the car itself

and, if you are doing a long run, make sure you only tack it in place first so that everythng lines up proplery before you even think of seaming it, anddon't seam a bit long length all in one go, the metal heats up and it distorts like a fooker