What type of cartridge should get for?

As some of you probably know I just bought a turntable, my problem I been out of this circuit for long time and when I was I used to use Audio Technicas AT-21, AT-15 and AT-13 if I remember right, I think that the AT-21 was Gold and the 13 was red. But I don’t remember why I pick them or even if I had a reason to pick them.
Well now that I bought a old turntable ( Optronica RP-3434) that I think originally come with a VM Cartridge that to be honest I do not have no clue what that means.
So the question is CAN I USED ANY TYPE OF CARTIDGE ON ANY TURNTABLE? Can I uses and MM or MC or MI ? Or what type of cartridge should I get for it?
If I could I would like to try a Grado MI... Can be done with this turntable?
Now if I can solve my first problem then the second show up..... What is the difference between Regular mount and P mount?
If I sound ignorant it’s probably because I’m on this matter, but with your help I’m planning to make the right decition.
Thank you
Paulo