My apologies in advance if I am not very clear (I am still programming in a rather childlish way).
I am trying to move from Eclipse to PyCharm (community version) and so far no issues with the editor or cloning from github. However I am having doubts on how to use classes and modules from an external project:
In Eclipse I would go to: Windows -> Preferences -> Interpreter -> Python Interpreter and over here add new folder, which would be the subfolder within Eclipse "workspace" folder where I am saving the project.
In PyCharm I am using File -> Preferences -> Project: Project_Name1 and over here I have the possibility to mark as sources (or excluded) all the project folders I want.
This brings me many doubts...
I imported several repositories (my own) from github and I set the option to keep open in the same window as the first (this option is new compared with eclipse but it gives me the same output with all the project within the package explorer).
However, when I got to
File -> Preferences -> Project:Only the first project appears independently which one I have selected. How can I modify the interpreter and/or dependencies for the rest?If I add a project folder to the project structure do I also need to modify the project dependencies?
Incidentally any guide or tutorial on the right so it imports are not broken with each new IDE or when the code is shared would be most welcomed.

