In your python file it looks for example like:
eng = matlab.engine.start_matlab()
eng.workspace['yourVar1'] = 1
eng.workspace['yourVar2'] = 'YourSecondValue'
You can also start this process directly from your python interpreter.
>>> eng = matlab.engine.start_matlab('-desktop')
>>> eng.workspace['yourVar1'] = 1
If you start the matlab session with the -desktop option Matlab's GUI is opened and you can directly see the changes.