Hi Nikola, the best way to export can be different depending on the particular printer being used so it is probably best to ask the service where you will be sending the parts to be printed what they want. Some may want the CAD model.

But for general advice especially for stl export you would usually want to have different parts be separated in the STL file, not positioned in place where they are touching each other.

STL format is pretty primitive, it's just a big heap of triangles without any connectivity information. So when multiple parts are overlapping the same space with each other it is difficult for the receiving software to figure out which part a particular triangle belongs to.

- Michael