Contrary to an earlier answer, ALL welding is fusion welding, be it gas Manual metal arc (MMA) MIG or TIG. The non-fusion thermal processes are brazing and soldering. Furthermore, a weld should be at least as strong as the base material that you are welding, in other words, if the welded joint were to be subjected to destructive testing, the plate, not the weld would fracture. So much for the theory - now to answer your question. I am assuming that the process you want to use is MMA (using a flux coated, consumable electrode in a holder). The first thing you will need is a welding plant and all the necessary Personal protective equipment. I would suggest buying a decent second-hand single phase industrial unit in preference to a new cheap one. The main difference is that the cheap plant will probably have a low Open Circuit Voltage, maybe as low as 30V which will only strike an arc with small diameter electrodes (say 2.5mm), The OCV is the voltage needed to strike the arc and is stated on the side of the electrode package. Normaly a set with an OCV of 60volts will be adequate. Furthermore, an industrial set will probably give a Direct current secondary (welding) output as well as (maybe) A.C. too. D.C. will give you the option of working with the torch either positive or negative (The work return being the other pole). Start practicing your welding by using 2.5mm electrodes to strike and break the arc, run at about 80amps. Do this on a peice of clean 5mm mild steel plate approx 100mm square. Once you have mastered this you can progress onto making weld runs right across your plate. Make sure you "Pull" the electrode, not "Push" as in MIG. Use a welding visor with about a number 11 filter fitted, not a hand sheild as this will leave both hands free. Once the arc is struck, keep it as short as possible - about 2mm. I could go on for ever, but think this will give you enough to get on with. - Good luck and enjoy your welding.