What an orbital is
An electron in an atom doesn’t follow a path. Quantum mechanics describes it with a wave function, ψ (psi). The square of ψ at any point says how likely you are to find the electron there. An orbital is one of the allowed wave functions, and its shape is the region where the electron is most likely to be.
The viewer picks a huge number of random points and keeps each one with a chance in proportion to ψ² at that point. The cloud that builds up is dense where the electron is likely to be and empty where it never is. Ink and crimson show where ψ is positive and where it is negative. The sign matters when orbitals overlap to make bonds.
Nodes
A node is a surface where ψ is exactly zero, so the electron is never found there. An orbital with principal quantum number n has n − 1 nodes in all. Some are spheres (radial nodes), some are flat planes or cones (angular nodes). The 2s orbital has one spherical node, which shows as a thin empty shell. The 2p orbital has one flat node through the nucleus, which is why it has two lobes.
Why hydrogen?
Hydrogen has one electron, so its equations can be solved exactly. In every other atom the electrons repel each other and the equations can only be solved approximately, but the orbitals keep the same shapes and the same names. That is why s, p, d and f are used for every element.