In the electron cloud, how do you know how many electrons to put on each line and why?

Answer 1

Please state your question in a coherent and complete form.

If you are referring to the electron orbitals in atoms then the answer is 2N^2 where N is the Principal Quantum Number. This produces the sequence: 2; 8; 18; 32; 50. But the electrons do not fill the orbitals in this order as the Energy Levels are Perturbed by the interaction with the nucleus and other electrons (and Polar Solvents such as water, ammonia etc). To see how they fill look at a Periodic Table of Chemical Elements and lists of electron structures for each element.
These figures come from the Quantum Mechanics applied to the Atom.