I made a gui app with python tkinter, I want to put a little mini little web browser inside my tKinter windown, without opening a new tab. How can I do that?
You can't. There is no widget in the tkinter library which allow you to display HTML. If you really NEED to use tkinter you could try tkinterhtml but it's weird and won't work for a lot of features (hyperlinks, images...)
If you just want to create a python app with a web interface, you'd better use a python web framework like flask or django.