Tkinter is not thread safe, it needs to run on your applications main thread. However when you call root.mainloop() your application won’t do anything more until the GUI window gets closed.
To do background tasks you create a new thread (or threads) to do them.
Feel free to comment if you can add help to this page or point out issues and solutions you have found. I do not provide support on this site, if you need help with a problem head over to stack overflow.