hello, in corners, you will shoot them one by one until your done, once you are, count how many corners you just solve, if it is even then no parity for them, but if they were odd, then you will have parity.
parity for corners is where 2 edges (4 in case of 4x4) are swapped, like if you do the J perm, 2 edges will be swapped, so you want to use the parity algorithm to swap 2 edges (r2 U2 r2 U2 u2 r2 u2) where the lower case letter is a move for a single slice, now before this algorithm you have to preform a setup move to get those edge oppisite of each other and oriented, if you do the J perm, the swapped edges will be UR and UB so a setup move will be R' U' R U, then proform the algorithm then unde by doing U' R' U R.
edges have diffrent parity of course, if you shoot edges odd number of times, then you will have r slice centers swapped and the rUF and rDB swapped, so preform this algorithm: r2 D' L' F ( l' U2 l' U2 F2 l' F2 r U2 r' U2 l2) F' L D
so this will be all about parity in 4x4 BLD.
centers you will have to practice them, use mr. Mike thread to understand them.
any questions you have just ask
thanks