[Krusinek]

Could someone explain this to me?

Thanks in advance !

[mjc123]

Seems pretty self-explanatory. Have you covered this stuff? Do you know what those dumb-bell shapes mean? Especially, do you know what is special about the xy plane for a pz orbital?

[Enthalpy]

This representation of orbitals draws a surface where the electron's probability density passes by some conventional limit. It's just a way to replace a fuzzy density by a sharp surface.

Inside the lobes, the density is bigger. Outside, it's smaller.

So as you have the picture with the lobes and the axes, you can figure at what positions the probability density is bigger.