Disclaimer: these notes were made from memory and may contain inaccuracies, please feel free to edit it.
MIG Welding
Metal Inert Gas (MIG) welding is the most commonly used approach. The machine feeds a line of metal (aluminum or steel, choose the one that is compatible with the base metal) out of the welding torch as you press the trigger. Here, Elijah demonstrates a perfect weld at first try:
⚠️ For all welding, you'll need to wear a flame resistant heat protective helmet, gloves, and a jacket. These will also protect against "sun burn" from welding. The helmets automatically decrease visibility when it detects light intensity beyond a threshold. In the video above, there is a jump cut where Elijah swaps out their helmet as it was not calibrated well and had reduced visibility even before welding began.
TIG Welding
Tungsten Inert Gas (TIG) welding uses a non-consumable tungsten electrode within the torch, that does not become part of the weld. Instead, the hot tungsten electrode melts the base metal, and an external metal filler rod is introduced by hand (kind of like soldering).
The TIG torch is controlled with a foot pedal, which also releases a shielding argon gas which keeps the molten metal from oxidizing during welding.
Stick Welding
Stick welding involves an external metal rod that contains flux, which protects the part being welded.
Spot Welding
Spot welding is like using a "sewing machine" (the video below illustrates this better), where the base material is clamped in the welding machine, and a current is passed through it to bind the metal together: