Fourth step: Do not drill too deep! The lower side of the groundwater is a watertight layer of some sort. Here it is marl (a kind of clay) of a greyish colour.
There is absolutely no need to drill into it and a waste of time and money (I paid for the meter drilled including the necessary amount of well casing). Also: the lowest part of the well casing is a filter. In most cases it is just the same pipe as the well casing with fine slits (3mm is enough here but your mileage may vary) but there are more expensive solutions, too. Any length of this filter inside the watertight layer if of little use and reduces the area where the groundwater can flow in.
Fifth step: case the well, that is: put a pipe into the hole to avoid the collapse of the whole. The drill string should be hollow to allow for it and needs a drill bit that you can screw out from above.
The pipe is something you can buy at e.g.: Amazon, at least that’s what I thought but despite a lot of hits for “Brunnenrohr” at amazon.de I got nothing at amazon.com for “well casing” except for the caps for the top.
Sixth step: clean up the whole mess before you go on 😉
Next: securing the well with the help of a bag of concrete.