hi Dimitrios, I'm not sure what levels Tableau has 'built in' for the Netherlands (in the UK we have Post Code [1st part], City, County), but Tableau needs to have these fields in the data in order to use them. In the example you've seen from T7, I imagine they were using the Superstore dataset which has State and City as fields in the data.
If you do need a level of geography that Tableau doesn't have 'built-in' for the Netherlands you can create your own 'custom polygons', based from the boundary file for that level.
The recognised geography levels only work one way, i.e. if you have city Tableau will generate Long and Lat for that city so you can plot, but if you had the Long and Lat for a city it wouldn't know what city that was.
Hope this makes sense, but please post back if not (or if you want some help with creating custom polygons)