Thonny is a Python IDE for learning and teaching programming.
On the first run you see a code editor and the Python shell.
Enter some Python code (eg. print("Hello world") ) into the editor and save the file with Ctrl+S.
Now run the code by pressing F5. You should see the output of the program in the Python shell.
You can also enter Python code directly into the shell.
Using the Debugger
You can see the steps Python takes to run your code. For this you need to press Ctrl+F5 to run the program in debug mode. In this mode you can advance the program either with big steps (F6) or small steps (F7). If you want to see how the steps affect program variables, then open global variables pane (View => Variables).
You can find more information, screenshots and a walk-through video at https://thonny.org.