hey guys think in this way
P: THE SENTENCE ON THE OTHER SIDE OF THIS CARD IS TRUE.
Q: THE SENTENCE ON THE OTHER SIDE OF THIS CARD IS FALSE.
now let us assume P is true which means Q is true.Now Q says P is false ,a contradiction,so P is false.
From above we concluded P is false so it means Q is false(what P says of Q is wrong).Now Q being false says wrong about P.Thus, P is true ,again contradiction.
This way we can start with Q and show that it too has no truth value(neither true nor false).
So, these statements mean nonsense although individually they seem to be logical statements.
Hence, it's all paradoxical
I hope i have conveyed it clearly :-)