What kind of folder type is this and how can I create this?
The name is basically a source folder hierachy of a project library I include. But I do not know what this actually is and how to create this. Looking at the file structre in Finder I don’t see anything. So I guess it must be some kind of link or so.
this is the symbol I try to understand -> 
Many thanks for your help!
This is a folder Icon.
Top Right + mark kind indicates it is a source.
Bottom Right with ! indicates that there are some warnings in your code. Look for the Errorlog to remove the warnings.
This is created by Eclipse, as soon as you create a new package, which internally creates a folder for each part of the package name.
Example: If you have com.android.myproject
then eclipse, will create a folder for Src, inside this a com foler, then inside this an android folder and finally myproject folder.