There are three basic types of electric welding in common use. In all
methods, an electric circuit if formed between the work and an electrod
which is handheld. The current that flows essentially determines the
thickness that can be welded.

MIG - Metal-Inert gas. A weld wire is fed into the joint automatically,
while an arc is struck on one end. The wire "burns up" at the same rate
it is being fed in. A blanket or shield gas is wafted over the weld site
to exclude oxygen. There are "gasless" Migs, where the wled wire
contains a flux core which de-oxidises the weld area. Mig is very easy
to use, but is not terribly controllable in amateur equipment. Amateur
Migs sets would probably top out at 4mm of mild steel, and only weld
things like aluminium with difficulty. Good method for RHS. Not good for
thick sections.

TIG - Tungsten-inert gas. The choice method for craft welding, TIG uses
a handheld torch with a sharpenened tungsten rod down the middle. Like
MIG, a shield of inert gas wafts from the torch to blanket the arc and
prevent oxidation. An arc is struck from the tungsten to the job which
then melts. A filler rod is then melted into the pool and welding
procedes along the joint. One of the best methods to weld thin section,
or aluminium. TIG sets can be very very sophisticated, and there are AC,
DC and combined sets. Small tig inverters can be used with MMA too.
Beautiful results, but needs great skill for good work.

MMA Metal-Metal arc. "Arc" welding. A metal rod encased in flux is used
in a handheld torch. The arc is struck from the rod to the job, the arc
melts a pool in the job, and drops of liquid metal fly off the tip.
2nd easiest method, works for thicker sections >4mm, needs no shield gas
or fancy torches. Can't be used on aluminium, VERY hard to use on thin
metal.

Get yourself a MIG for around 100 quid these days. I have an SIP MIG
which is pretty good. If you go this route you do need a gas bottle,
which is a (lowish) annual rental. If you weld steel, get a gas called
Coogar rather than the cheaper (crap weld) carbon dioxide.

Steve

if youre welding up to 5mm plate youll need a 150amp mig welder .

this is about as big as you can run on 16amp mains .
if you have a 32amp socket you can use then a 200amp mig will work nicely .

i doubt though that youll require any more than a 150amp welder for almost all
you want to do .

gas , there are 2 types youll use for steel welding , firstly  and cheapest is
CO2  carbon dioxide .

this is obtainable in refillable bottles from welding supplies outlets and cost
is £30 for the first full bottle and then about £9 per refill exchange of
bottle .
this is SEALEY make .

there is now also a small cylinder available , argon+co2 mix , this is around
£30 bottle rental for 3 years and around £10 for each  refill, but these
cylinders hold 10x the gas the sealey bottles do .

co2 will suffice for the majority of welds , some say it cools faster and dont
like it but i doubt youll notice the difference between the 2 gases on offer .

as for wire youll use either 0.6mm or 0.8mm PLW [precision layer wound ] in 1kg
or 5kg reels .

0.6mm is used for welding thin plate , ie on car body repairs, but 0.8mm is a
good combination between thin and thicker plate ability .
you can weld thicker plate with 0.6mm but it will need to have wirefeed speed
high .

0.8mm will also not tend to stick or clog up in the liner in the  torch  and
make a birdsnest on the feedrollers .

for just thin plate welding you can use a 100-130amp mig ok.

one word of advice , if you buy a 150amp mig , then try to get one which uses a
euro adapter for the welding torch and use a binzel or parweld MB15  torch in
it .
you can also use an MB25 torch , these i buy for £30 .

spares are cheap for these torches , i pay 20p per welding tip , but i buy  in
large numbers to obtain this price .

as for gas regulator youll need a "single stage dual gauge " type .

hope thats of help to you .