The first thing you need to do is purchase a MIG welder and the proper gear. I suggest to first practice the MIG welder on scrap metal before moving on to the real thing. While MIG welding is probably one of the easiest types to welding to learn, you should still practice before using it on your favorite project.
Always purchase the right safety gear. A welding helmet should be the first item on your list. I would recommend a battery operated, auto darkening welding helmet. You will also need to get proper clothing and gloves. Basically, you should cover up your entire body. MIG welders throw off sparks which can burn your skin.
Next, you should pick a suitable location to begin welding. A large concrete slab, like your driveway, is always a good choice. Always remember that there is a fire hazard when using these welders. The welder will create sparks and generate heat, so you should always keep a bucket of water, or fire extinguisher nearby.
Now you are ready to start operating your MIG welder. There are three main things to consider which will determine how good your weld is. These are the tip voltage, rate of feed and how fast you move the tip.
The voltage controls the penetration, while the feed rate of the wire will adjust the arc length and the speed at which you move the tip controls the transfer of metal to your work area. If the voltage is lowered, the weld will sit on top and too high will result in just creating a hole. This is why you need to practice, to get a good feel for it.
Now you need to find a good speed to move the tip. If the tip moves too fast, you will hear loud popping noises and lose the arc. If you move it too slow, the tip might melt and fuse to your work, which is a real hassle. Again, practice is critical and it is not really that hard after a few tries.
Now that you have the right voltage, feed rate and feel comfortable with using the MIG welder, it is time to work on that project. Remember, the key is to keep the tip moving all the time. It will seem tricky at first, but after a while and more experience, you will be welding all sorts of things!