Electro-magnetic waves

Good afternoon everyone,
Today i was studying about Electromagnetic waves as a part of Structure of an Atom, Grade XI. My brain-aching question is, What does it mean if the electric field is going from x to y axis , and magnetic field doing the same during the propagation of Em waves. I can imagine a particle moving up and down (vibrating) during the transfer/propagation of a sound wave but i am unable to imagine electric or magnetic field doing this. Neither was I able to find any animation or visual that would help me do so.
Keeping in mind this is electric field:


and this the magnetic field:

and let me apprise you that this is the propagation of the wave, the changes taking place in their fields with respect to time passing by and not the actual diagram of the change taking place in the structure of their fields. If the magnitude is also varying, you can share that as well.