Quantum numbers and Aufbau principle

Maybe someone asked this before, but I've searched on this forum and found nothing that can help me.

My question(s):

I know the Bohr model isn't totally right and that electrons are in orbitals (s, p, d, f..).

The exact location of an electron is being specified with 4 quantum numbers:

n I get that one, say n=4

l Dot get that exactly, but I know that when n=4, the possibilities for l are 0,1,2 and 3

m For every l: all integers bitween -l and +l

s +1/2 or -1/2 something with the spin?

I don't know if it is really necessary to know what those quantum nubers exactly are?

Okay, now they're named by 1s, 2s, 2p, 3s etc.

are they named like the numbers **1**s, **2**s, **2**p, **3**s are the n's?

and the letters, 1**s**, 2**s**, 2**p**, 3**s** are the l's? (l=0 -> s, l=1 -> p, etc?)

If that's right, I think i get that.

My last question, Aufbau priciple, I think it's so weird :(

why has for example 3d a higher energy level than 4s? and does someone have a hint how you can remember that?

I'm also wondering how you must distribute the electrons in the orbitals (say, you're working with O (8 electrons)), I know it has something to do with the quantum numbers, but what?

I hope someone has enough time to help me out.

:D