What is the difference between the electron shells, the subshells, and the orbitals?

Electron shells are the discrete energy level in an atom where we can find electrons, it is same as electron orbit.If we further divides energy level of a electron shells then it is called Electron subshell, it is same as electron orbitals, furthermore the classical figure shown in textbooks for s,p,d,f are actually the area where the probability of finding an electron is maximum

There is one s orbital, and there are three p orbitals, five d orbitals, and seven f orbitals. thus, the answer is b. do not confuse the number of orbitals in a subshell with the number of electrons the subshell can hold. each orbital can hold two electrons, so the capacity of an nf subshell is 14 electrons.

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.