The experiment shows that
There exist two kinds of charges: positive (+) and negative (-) Same sign charges repell each other, opposite sign charges attract each other
In an electric field: A negatively charged particle is attracted by the positive plate A positively charged particle is is attracted by the negative plate.
In a magnetic field: A positively charged particle is deviated as shown A negatively charged particle is deviated in the opposite direction
The images are borrowed from the "bible" of Chemistry: College Chemistry (2nd edition) from Linus Pauling