I used to work at a place that built brewery equipment and we were always trying to bring labourers up to apprentice as welders. They would watch a welder for a bit to get the idea of what the welding should look like. Then I would give them a pile of scrap to work with and set up a few "T" joints to try first. I would do one or two and then let them try. After they did a couple of welds, I would let them know what to try to help out in getting their quality up. I would generally spend 4-6 hours working with them then let them have a try themselves for the rest of the day. Although, keep an eye on them so they don't get side tracked too much. After a day or two of practicing they were usually ready to try some real welding out, but not on anything important of course! Most guys that had any talent for it were up and running within about 2-3 weeks. It usually didn't take too long for them to catch on. We would then assign jobs according to their abilities and maybe even get an apprenticeship for them after 6 months or so.

As far as teaching someone to TIG weld for a day or two, that would be a tough thing to do unless they have some welding experience already. They will need a bit of time to figure it out.

Hope this may have helped?