A shell contains sub shells (s,p,d,f) and within these subshells are orbitals (you only need to know about s, px, py, pz I believe). Each orbital can hold two electrons of opposite spin. Elements in the S block have their outermost electron in an S subshell, likewise for P, D or F block elements.
An example of a P block element would be Chlorine, it's outermost electrons are in a P subshell which contains 5 electrons (as it is 5 along the p block on the periodic table). It's electron configuration would be 1s2, 2s2, 2p6, 3s2, 3p5. If you look on the periodic table you can easily see the very last of an elements electron configuration. i.e Chlorine is in period 3, 5th along the P block, hence it's outermost subshell is 3p5, and all subshells before this are also filled (some exceptions to this rule, but not needed for AS).
As a shell consists of multiple sub-shells the maximum number of electrons is given by 2n^2, where n is the shell number;
n=1, 2
n=2, 8
n=3, 18
n=4, 32
As already mentioned, any orbital can only hold 2 electrons, but each subshell has a different number of orbitals, so an S subshell has an S orbital only, a P subshell has 3 P orbitals all at right angles to eachother, D subshell has 5 orbitals (shape/location not needed)
Hope this clears up most questions you had but I'm glad to help if there's anything extra.