Hey tube.
wid 79 is right - vee butt prep your weld. Or dont bother but leave a small gap (1 mm) between the parts when you tack up. If you are getting a lot of spatter, turn the current down. If you are getting porosity, turn the gas up. If you are using co2, don't. Use an argon mix.
From your pics it looks as if you are not getting adhesion, so slow down the wire feed a little. Penetration just means the filler is getting to the bottom of the weld area. Adhesion is the sticky bit that matters. you need both for a good weld.
With MIG, if your welding is quiet, smooth and not too splattery, you have everything ok. Otherwise, experiment until it works. Get some scrap and practice. If you want to learn to weld, there's no other way! (tried plastering recently?)
Back in the olden days (when maggie T was young, before we all went on the dole) we used to use co2 as standard for heavyish plate - 4mm or more. But we always used a heater for the gas. As co2 leaves the bottle the reduction in pressure cools it like buggery, hence the frost on the bottle, all you beer pump gas users. Migs dont like this at all, and give very nasty welds. Get a heater, or stick to co2/argon mix. Believe me.
Oh yeah - if you want to avoid paying those ridiculous rental charges for gas, find yourself an empty argoshield bottle from the local dodgy geezer, hold onto it while you set up a rental agreement with BOC, then after a reasonable amount of time, take the empty back to the BOC hire centre and take your bottle off hire. You still have to pay that stupid handling charge, but if you are a low quantity user, you pay NO MORE RENT, until you go through the process again.
I take no responsibility for anybody acquiring stolen BOC bottles.... but it does make sense.