If we think of electron configurations as an electron's "address".  The s, p, d, and f tell us the type of house they live in and refer to the shape of the orbital where we find a particular electron.

Each orbital, no matter what the type, can only hold 2 electrons.  When we look in any one principal quantum shell (i.e. n=3), we can have multiples of some orbital types.  There is only 1 s orbital in each shell, but there are three p orbitals, 5 d-orbitals and 7-f orbitals.  We don't have any d orbitals until the n=3 level and no f-orbitals until n=4

The SPDF refers to how the electrons are configured.  The S, P, D, and F are orbital names that are short for sharp, principal, diffuse, and fundamental.  I actually found you a useful chart you can use that shows the electron capacity of each.

http://www.edu.pe.ca/kish/grassroots/chem/electron.htm