On your welder... You didn't buy a MIG welder, did you? Either that, or you didn't go and get the gas bottle that goes with it, and have it turned up high enough.
I can tell, those welds look like mine did when I first started, and was working with a stick welder and then a wire feed welder without a gas feed. Now I have a MIG welder, and it is literally hot glue for metal it's so easy.
The spatter and brown scorching you have is indicative of air (oxygen) at the point of arc, and that causes several problems. The plasma arc burns the air, splitting the oxygen and hydrogen apart, and the oxygen high-speed oxidizes what you are welding, ruining the welds from the inside out. I'm sorry to say, but those connections will never hold for long. Mine had twice as much slag on them, looking just as spattered... And only lasted about 6 months under the car.
Also the oxygen expands as it is burning, causing holes and pores to develop in the liquid metal, further weakening it. That connection will leak exhaust through those holes, and the humidity of a cold-start will get in there and rust it out from the inside too.
If you haven't gotten the gas kit yet, go get it. Look in the Yellow Pages for your local Welding Supply or Praxxair distributor. They sell all sorts of supplies, and Praxxair is one of the largest gas suppliers. You can get the hoses and regulator from them, and buy various sizes of tanks too. Don't rent the tank, its stupid. Buying it outright is better, you can refill it whenever you need to, and refills are cheap. Get an 80/20 Co2/Argon mix, its the easiest to weld with next to pure argon, but a lot cheaper. I bought an 80 cubic foot tank (size of a dive cylinder) and that will probably last me darn near forever. Its about $30 to refill that, but I've burned through a LOT of welding wire so far, and haven't put a dent in the regulator's meter reading.
If you aren't going to be welding a lot, I would suggest something in the 20-40 cubic foot range.
Get some scrap junk to practice on, you will eventually learn that the voltage setting is your "heat" setting, and you want it hot enough to start to melt what you are working on, so that if you stay moving it's fine, but sit in one spot... And make holes. Start with lower voltages until you get your speed up, lower voltage = lower bead progression. The feed speed is just that, but you want it fast enough to keep a continuous arc struck. Your weld shows nowhere near a continuous arc, which is why you have spatter everywhere. Also, constantly breaking the arc doesn't allow the subject to heat properly, so the welding wire can't bond properly by "soaking in" to the subject. The gas will help a lot with this. You want to start the gas flow off as low as possible (to preserve the gas) but IIRC, I have my rig set on about 5-7 or so for the output. I can't remember what the scale is on the regulator, I just remember those numbers. For learning, you will probably want to use more gas initially to make it easier. I've been welding for a couple years now. Once you get a nice fat arc going, listen to the sound it makes, compared with the spatter-fest you have now. That sound is your best indication of a good weld.
Good luck!
Beware the welding monster... Eventually you will figure this out, then all of a sudden you will have the desire to start sticking metal together everywhere for everything... Its a curse!
