That's a wide-open question!
There is a lot of advice on TIG welding in s.e.j.w. Superb archive
access available through Google at
Look for Ernie Leimkuhler's advice on torch-handling technique and
currents. Sttarts of with "amp per thousandth of inch of thickness"
then adjustments for... And practice maipulation using pencil and
washer (you can left-hand TIG without crashing the tungsten if you
have done this exercise first!).
size of tungsten
size of filler rod
They need to be correct otherwise you will not do well at all.
Th weld pool when aluminium (aluminum!) TIG welding - it's an amazing
clean silver liquid appearance, with the glowing tungsten above
reflected in it.
Don't know so much about aluminium, but a lot of beginners overheat
the liquid metal and run into chronic problmes enough to make a grown
man cry, until they learn to control temperature.